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Upcoming Colloquia

Department of Physics & Astronomy                                                                                  Colloquia Archive

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Fan Zhang

Dr. Fan Zhang

University of Texas at Dallas

DATE/TIME: 05/06/2022  |  2-3PM MDT

Location: Zoom Link

Short Biography:

Dr. Fan Zhang obtained his bachelor’s degree from Univ. of Science and Technology of China in 2006 and PhD from Univ. of Texas at Austin in 2011. He did his postdoc at Univ. of Pennsylvania before joining Univ. of Texas at Dallas as a faculty in 2014, where he is an associate professor now. Zhang’s research focuses primarily on topological matter, correlated electrons, and 2D materials.

Higher-Order Topological Matter

Recently, a novel class of topological insulators and superconductors (TI and TS) coined "higher-order (HO) TI and TS" has become a major topic in condensed matter physics. A HO TI or TS hosts protected gapless states on boundaries of more than one dimensions lower, such as hinge and corner states. I will introduce three prototypes that we proposed in 2012, 2018, and 2020, respectively, featuring unique physics of TI and TS, in two and three dimensions, with and without time-reversal symmetry. I will also discuss the experimental efforts in realizing these rare phases of matter in solid-state systems and particularly in the unique Bi4X4 (X=Br,I) family, which not only represents the quasi-one-dimensional generation of TI but also brings the excitements to the room temperature and the correlated regime.

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Dr. Ashish Mahabal

California Institute of Technology

Date/Time: Friday April 29th, 2022

Location: Physical Sciences 234 | 4:00pm

Short Biography:

Ashish Mahabal is an astronomer and lead computational and data scientist at Caltech in Pasadena, CA where he has been working since 1999.  Before that he got his PhD in Astronomy at the Inter-University Center for Astronomy and Astrophysics (IUCAA) in Pune India in 1998. He has worked on many large sky surveys over the last two decades, and currently leads the machine learning group for the Zwicky Transient Facility (ZTF) with a special interest in classification. He also applies data science techniques to early detection of cancer and other medical data in collaboration with NASA's Jet Propulsion Laboratory. He chairs the Astroinformatics and Astrostatistics working group at the AAS and the corresponding commission at the International Astronomical Union.

Machine Learning in the Era of Time Domain Astronomy

Astronomy surveys like the Zwicky Transient Facility have been leading to discoveries that are orders of magnitude more than just a decade ago. The discoveries range from the Solar System (comets, NEAs etc.) to Galactic science (CVs, YSOs, binaries etc.), to extragalactic (distant supernovae, AGN, TDEs) and possible EM counterparts to multi-messenger transients. We will provide an overview of the plethora of discoveries, and the ongoing work. We will describe our plans for ramping up discoveries even further with the aid of machine
learning, especially by combining the archives with fresh alerts.  With newer surveys, as we go fainter, cover more wavelengths, and go multi-messenger, more novel objects will be found. The rarity of these objects will both push the boundaries of our understanding, and also, due to the lack of statistically significant samples sometimes lead to premature claims, especially when using cutting-edge machine learning. We explore some aspects of time domain astronomy and its inherent biases, and comment on the requirement to explain the results through various techniques often involving post-hoc interpretability.

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anand bhattacharya

Dr. Anand Bhattacharya

DATE/TIME: 04/22/2022; 2-3 PM

Location: https://uwyo.zoom.us/j/98734469058

Short Biography:

Anand Bhattacharya is interested in exploring novel phenomena that emerge at interfaces of correlated and topological materials. These include spin and charge transport properties, and novel forms of magnetism and superconductivity.  His group synthesizes materials using molecular beam epitaxy and other approaches and explores their properties using a broad range of techniques that reveal their electronic and magnetic properties. Anand grew up in India and got his undergraduate education at the Indian Institute of Technology at Kanpur in Physics. He then moved to the United States for his Ph.D. at the University of Minnesota. He has been at Argonne in 2004, first as a visiting scientist, and since 2006 as a staff scientist.  He was elected as a Fellow of the American Physical Society in 2019.

Superconductivity at interfaces of KTaO3

In this talk I will discuss the recently discovered superconducting electron gas at interfaces between KTaO3 (KTO) and insulating overlayers. The superconducting Tc can be as high as 2.2 K, about an order of magnitude higher than in the LaAlO3/SrTiO3 system. The superconductivity at KTaO3 interfaces has a number of striking features. Firstly, it is strongly orientation selective. While the interfacial electron gas at the KTO (111) interface has a Tc as high as 2.2 K, for the (110) interface the Tsaturates at about 1 K, and the (100) interface remains normal down to the lowest temperatures measured. Secondly, the superconductivity is strongly tunable – the Tc can be varied by both chemical doping and via electric field-effect gating. Notably, for KTO (111) interfaces,  Tc varies linearly with the carrier density as determined by the Hall effect, remaining superconducting down to very low carrier densities. These properties point to a highly tunable two-dimensional interfacial superconductor that may have relevance in superconducting electronics, while also suggesting an unconventional mechanism for superconductivity. I will focus on a theoretical proposal where we suggest that an inter-orbital pairing mechanism can address key aspects of superconductivity at KTO interfaces.

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meredith macgregor

Dr. Meredith MacGregor

University of Colorado Boulder

DATE/TIME: Friday, April 22, 2022 | 4:00PM

Location: Physical Sciences 234

Short Biography:

Dr. Meredith MacGregor is an assistant professor in the Department of Astrophysical and Planetary Sciences (APS) at the University of Colorado Boulder. Her research group uses multi-wavelength astronomical observations to explore the formation and habitability of planetary systems. Her work has been widely covered in the popular press including Scientific American, Science News, and National Geographic. She is a Scialog Fellow, the Co-Chair of the NASA Infrared Science Interest Group, and the Associate Director of the Center for Astrophysics and Space Astronomy (CASA). Previously, she was an NSF Astronomy and Astrophysics Postdoctoral Fellow at the Carnegie Institution for Science, Earth & Planets Laboratory in Washington, D.C. after completing her Ph.D. in Astrophysics at Harvard University in 2017.

How to Form a Habitable Planet

More than 20% of nearby main sequence stars are surrounded by debris disks, where planetesimals, larger bodies similar to asteroids and comets in our own Solar System, are ground down through collisions.  The resulting dusty material is directly linked to any planets in the system, providing an important probe of the processes of planet formation and subsequent dynamical evolution.  The Atacama Large Millimeter/submillimeter Array (ALMA) has revolutionized our ability to study planet formation, allowing us to see planets forming in disks and sculpting the surrounding material in high resolution.  I will present highlights from ongoing work using ALMA and other facilities that explores how planetary systems form and evolve by (1) connecting debris disk structure to sculpting planets and (2) understanding the impact of stellar flares on planetary habitability.  Together these results provide an exciting foundation to investigate the evolution of planetary systems through multi-wavelength observations.

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roopali kukreja

Dr. Roopali Kukreja

University of California, Davis

DATE/TIME: Tuesday April 12, 2022 | 1:00PM

Location: Classroom Building 118

Short Biography: 

Roopali Kukreja joined Materials Science and Engineering department at UC Davis as an Assistant Professor in Fall 2016.  She received her B.S. in Metallurgical Engineering and Materials Science from the Indian Institute of Technology Bombay in 2008 and then her M.S. and Ph.D. degrees in Materials Science and Engineering from Stanford University in 2011 and 2014, respectively.  Prior to her appointment at UC Davis, Kukreja worked as a postdoctoral researcher at the UC San Diego, with Profs. Oleg Shpyrko (Physics Department) and Eric Fullerton (Center for Magnetic Recording Research). Her research interests at UC Davis focuses on ultrafast dynamics in nanoscale magnetic and electronic materials, time resolved X-ray diffraction and imaging techniques, thin film deposition and device fabrication. She is recipient of Melvin P. Klein Scientific development award (2015), AFOSR Young Investigator Award (2018), NRC Faculty Development Award (2019), DOE Early Career Award (2021) and NSF Early Career Award (2022).

Imaging ultrafast and ultrasmall: Unraveling magnetic and electronic behavior using time-resolved coherent x-ray scattering

Ultrafast laser control of magnetic and correlated materials has emerged as a fascinating avenue of manipulating magnetic and electronic behavior at femtosecond to picosecond timescales. Ultrafast manipulation of these materials has also been envisioned as a new paradigm for next generation memory and data storage devices. Numerous studies have been performed for both magnetic metallic systems as well as complex oxides to understand the mechanism underlying laser excitation. However, it has been recently recognized that spatial domain structure and nanoscale heterogeneities can play a critical role in dictating ultrafast behavior.  In this talk, I will focus on utilizing time-resolved x-ray scattering and nanodiffraction studies to study spatial texture dependent dynamics in magnetic multilayers and correlated systems. I will describe our recent experimental studies using emerging synchrotron techniques and free electron laser such as European XFEL and FERMI. In magnetic multilayers, we uncover a symmetry-dependent behavior of the ultrafast response. Labyrinth domain structure with no translation symmetry exhibit an ultrafast shift in their isotropic diffraction peak position that indicates their spatial rearrangement. On the other hand, anisotropic domains with translation symmetry do not exhibit any modification of their anisotropic diffraction peak position. I will also show that spatially dependent ultrafast response is observed in complex oxides such as rare-earth nickelates. Theis intriguing observation suggests preferential, texture-dependent paths not only for the transport of angular momentum, but also for structural rearrangements. These measurements provide us with a unique way to study and manipulate spin, charge and lattice degrees of freedom.

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Dr. Dali Sun

North Carolina State University

DATE/TIME: 03/25/2022;  2-3PM 

Location: Zoom Link

Short Biography:

Dr. Sun’s research interests are in spintronics and optoelectronics of organic semiconductors, magnetic thin films, and organic-inorganic hybrid perovskites. It includes the studies of organic spin valves, organic light-emitting diodes, hybrid perovskite optoelectronic/spintronics devices, and their device physics. The Sun Research Group at NC State focuses on exploring novel routes for spin injection and detection, magnetic field effect, spin Hall effect and their applications in molecules, polymers and newly emerged materials. Dr. Sun is one of the pioneers who launched spintronic studies in hybrid perovskite materials.

Spintronic Terahertz Emission from Two-Dimensional Hybrid Metal Halides

Terahertz (THz) technologies hold great promise for the development of future computing and communication systems. The ideal, energy-efficient, and miniaturized future THz devices should consist of lightweight, low-cost, and robust components with synergistic capabilities. However, a paucity of materials systems possessing both these desirable attributes and functionalities has made device realization difficult. Two-Dimensional Hybrid Metal Halides (2D-HMHs) have been shown to allow for facile and economical, solution-based synthesis while still maintaining high energy conversion efficiency, chemical flexibility, and defect tolerance. These attributes make them ideal candidates for high-performance THz communication applications. Spintronic toolkits, on the other hand, can serve as an effective ‘control knob’ for future THz devices when interfacing HMHs with ferromagnetic (FM) materials, taking advantage of the fast relaxation of spin (akin to a ‘switch’) and the couplings between magnons, photons, and spins. The broken inversion symmetry and resulting giant Rashba state formed at the 2D-HMH surface allow for the spintronic control of intensive THz generation. In this talk, we will present the observation of spintronic-THz radiation in 2D-HMHs interfaced with a ferromagnetic metal, produced by the ultrafast spin current under femtosecond laser excitation. Our work demonstrates the capability for the coherent control of THz emission from 2D-HMHs, enabling their promising applications on the ultrafast timescale as solution-processed material candidates for future THz emitters.

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Dr. Shulei Zhang

Case Western Reserve University

DATE/TIME: Friday 3/11/22   2PM

Location: Zoom Link

Short Biography:

Shulei Zhang received a Ph.D. in Physics from the University of Arizona in 2014. Following postdoc research at the University of Missouri and Argonne National Laboratory, he joined the Case Western Reserve University as an assistant professor of physics in 2019. His current research interests include: coupled spin and charge transport in topological quantum materials, magnetization dynamics and magnon transport in ferromagnetic/antiferromagnetic materials, magnetic skyrmions as well as skyrmion-induced charge transport, and chiral surface/edge magnetoplasmons associated with Berry phase effects.

Nonreciprocal spin and charge transport in magnetic and topological materials systems

Experimental characterizations of transport phenomena in topological and magnetic materials have mainly been based on linear responses of spin and charge carriers to the applied electric field or current. Far less well understood are emerging nonreciprocal response effects that, in principle, can also be hosted in these materials systems, due to spin-orbit interaction, broken inversion symmetry, and/or band topology.

In this talk, I will present our theoretical works on three representative nonreciprocal transport phenomena that have recently been of particular interests: 1) a unidirectional magnetoresistance effect in conducting ferromagnet|nonmagnet bilayer systems, which is analogous to the current-in-plane giant magnetoresistance effect, but with a current-induced spin density – as opposed to a ferromagnetic metal layer – playing the role of a spin polarizer, 2) a bilinear magneto-electric resistance effect in 3D topological insulators, which may be deemed as a nonlinear version of spin-to-charge conversion, arising from spin-momentum locking of surface Dirac fermions and time-reversal symmetry breaking, and 3) a nonlinear Hall effect in Weyl semimetals, a new transport signature of chiral anomaly – which, in the presence of non-perpendicular electric and magnetic fields, creates an effective chemical potential difference between a pair of Weyl nodes with opposite chiralities and thereby becomes detectable in the nonlinear response regime.

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Dr. Kevin Grazier

Masten Space Systems

See Below for Dates/Times

Short Biography:

Dr. Kevin Grazier is currently the staff scientist at Masten Space Systems, a private space company based in Mojave, CA. Dr. Grazier earned undergraduate degrees and his MS from Purdue University and did his dissertation on planetary dynamics at UCLA. His primary research area involves numerical method development and large-scale computational simulations of Solar System dynamics and evolution. For 15 years Grazier was a research scientist and science planning engineer at NASA’s Jet Propulsion Laboratory on the Cassini/Huygens Mission to Saturn and Titan. He was the Investigation Scientist for the Imaging Science Subsystem, the main camera aboard the spacecraft, and wrote mission planning and analysis software that won both JPL- and NASA-wide awards. While full-time at JPL, Grazier also taught astronomy classes at Santa Monica College and UCLA. After leaving JPL, Grazier spent two years teaching at the U.S. Military Academy in West Point, NY. Dr. Grazier has also worked in the Hollywood entertainment industry for over two decades, serving as the science advisor for several television series and feature films. He was the science advisor on the Syfy Channel series Eureka, Defiance, and the Peabody-Award-winning Battlestar Galactica. Most recently he worked on the Apple TV+ series Foundation. He was also the science advisor for the movies Gravity, Pirates of the Caribbean: Dead Men Tell No Tales and, earlier this year, Escape Room: Tournament of Champions. He also wrote the pilot episode of the science edutainment series Space Quest: A Journey Beyond Space. Grazier is also the co-author for the Hollyweird Science series of books that explore the depiction of science, scientists, and the culture of science in TV and film. He currently resides in Huntsville, AL, with a menagerie of animals.

Public Talk 12/9 @ 7pm CR 118

Hollyweird Science: The Relationship between Science and Story in TV and Film

When there is a science mistake in a film or a favorite television show, do you notice? Does it pull you out of the drama? Does it make you angry? Does it leave you asking, “Why did they have to do that? It was easy enough to get that right if they’d just gone through the effort!”? It turns out that Hollywood has been going through the effort. Now more than ever, Hollywood productions are incorporating science advisors to help them get the science as right as possible, while still telling the stories they want to tell. The National Academy of Sciences places such an emphasis on science accuracy in TV and film that they have even opened an office in Los Angeles. Known as the Science and Entertainment Exchange, they provide free science consulting to creatives in the entertainment industry to raise the bar for science discourse in TV and film. Dr. Kevin Grazier has been a science advisor for many television series (Battlestar Galactica) and movies (Gravity). He is also the co-author of the Hollyweird Science series of books that explore the depiction of science, scientists, and the culture of science in TV and film. He will discuss the relationship between science and story in TV and film, and why sometimes it is important to get it right, while there are other instances where productions intentionally get the science wrong.

Astronomy Colloquia 12/10 @ 4pm in PS 234

Jupiter’s Role as a Cometary Shield Revisited

It has been widely reported, even on popular astronomy television series, that Jupiter has a profound role in shielding the terrestrial planets from comets raining in from the depths of space. The “Jupiter as a Shield” concept evolved such that some claimed that a jovian planet is a near-requirement for the evolution of life on Earth and in the formation of exo-Earths. The origin of this concept is often credited to a 1994 paper by George Wetherill in which he reported on the result of numerical simulations, but although Wetherill used the term “Jupiter barrier,” he never claimed that Jupiter acts as an impenetrable comet shield. His numerical methods have also since been shown to have failure modes that occur often. To evaluate whether Jupiter shields Earth, we re-created the work of Wetherill, and discovered that not only is Jupiter not a credible shield, it is at least as likely to divert non-threatening comets and asteroids into the inner Solar System.
Following on from that work, using techniques inspired by the type of Big Data analytics used by Hollywood and large retail firms, we mined data sets generated from that research to glean further insight into the many paths planetesimals may take as they wend their way throughout the Solar System—which includes a description of the mechanism for how Centaur objects are converted into Jupiter Family Comets. These results have wide-ranging implications, including a plausible mechanism for how the K-Pg impactor may have made its way to Earth.

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Dr. Leszek Malkinski

DATE/TIME: 12/10/2021; 2 PM

Location: CR 222

Short Biography:

Dr. Malkinski received his PhD in Physics from the Institute of Polish Academy of Sciences in 1991. He had several postdoctoral positions working among others at CERN, Switzerland, PTB, Germany, University of New Orleans and University of Colorado at Colorado Springs. He accepted Assistant Professor position at the University of New Orleans in 2002. He is currently Professor of Physics and Materials Science and a chair of the Department of Physics and a member of the Advanced Materials Research Institute. His current research is focused on thin film technology for energy harvesting. He is an author of over 100 articles and an editor of 2 books.

Ferroelectric Photovoltaics

All conventional solar cells use electric field at the interface between two doped semiconductors to drive electrons and holes, generated by absorption of photons of sunlight, in opposite directions which results in solar current. I will present a new concept of conversion of the solar energy into electric current which involves tunneling of photoelectrons through a thin ferroelectric layer deposited on top of pure semiconductor where photoelectrons are generated. Our initial results in Si/(Si-doped hafnia) system showed that electron-hole pairs generated by absorption of light in indirect bandgap semiconductor (Si) were separated by electric field within the ferroelectric layer and formed a photocurrent. Advantages of the next generation solar cells are that doping of semiconductors is not necessary and they can potentially provide larger voltage than the conventional cells based on silicone.

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Dr. Roland Haas

National Center for Supercomputing Applications

DATE/TIME: Friday Dec. 3, 2021; 4PM MST

Location: Physical Sciences Room 234

Short Biography:

Dr. Roland Haas received his PhD in Physics from the University of Guelph in 2008. After PhD, he has hold post-doc positions at Georgia Tech, Caltech, and the Max-Planck Institute for Gravitational Physics, also known as Albert-Einstein-Institute (AEI). He joined National Center for Supercomputing Applications (NCSA) as a senior research programmer and numerical relativist in 2016. His research is on relativistic astrophysics and numerical relativity, including supernova, neutron stars, and binary black holes. He has been using and developing the Cactus framework and Einstein Toolkit since 2011. He is now the lead principal investigator for the Einstein Toolkit grant with 6 partnering institutes (UT Austin, U of Idaho, LSU, RIT, UIUC, UWYO). 

Present and future astrophysics simulations using the Einstein Toolkit

General relativistic numerical magneto-hydrodynamics simulations are used to simulate the merger of neutron star and black hole binaries, disks around black holes, as well as supernovae. Driven by multi-messenger detections of gravitational waves and electromagnetic signals new groups that did not in past engage in these simulations are joining the simulation effort. These simulations however combine demanding hydrodynamics simulations using high-resolution shock capturing schemes with a fully general relativistic treatment of gravity cannot be developed by single researchers anymore. Instead, the Einstein Toolkit is a community driven framework for numerical these astrophysics simulations that is used by many group throughout the world.

I will first present an overview of current work using the Einstein Toolkit to simulate neutron star mergers, accretion disks, and binary black hole mergers, focusing on the aspects of the toolkit that facilitate these simulations. I will highlight the scientific results obtained using the toolkit by different researchers around the world.

In a second part I will introduce the next generation mesh refinement driver for the Einstein Toolkit: CarpetX. CarpetX leverages the AMReX mesh refinement library that is being developed as part the Exascale project. It improves on the current mesh refinement driver, Carpet, by supporting fine grained mesh refinement to track features in the simulations and native support for GPU accelerated computing. I will present an outline of CarpetX's design and current capabilities.

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pratibha dev headshot

Dr. Pratibha Dev

DATE/TIME: Friday 12/03/2021; 2 pm (MST)

Location: Zoom Link

Short Biography:

Pratibha Dev is an Associate Professor of physics at Howard University. In 2009, she obtained her Ph.D. in theoretical Condensed Matter Physics from the University at Buffalo, NY. Before joining Howard in 2015, she worked as EMPOWER fellow (Irish Research Council fellowship) in University College Dublin, Ireland (2010-2012) and as National Research Council fellow (2012-2015) in the Naval Research Laboratory in Washington DC. Her group uses atomistic-level simulations to determine properties of materials, covering a broad range of applications, spanning the fields of Condensed Matter Physics, Material Science and Quantum Chemistry. Her current research focus is on the fundamental physics of novel quantum materials and multi-ordered materials.

Two-Dimensional Layered Materials: Effects of Substrates/Layer Thickness

Research in two-dimensional (2D) crystals started with the isolation of graphene in 2004, which was soon followed by the discovery of many other 2D-materials, such as hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs). Earlier theoretical works that studied 2D crystals, ignored the effect of substrates and the ambient gases on the properties of 2D materials. However, as the 2D-crystals are surface-only structures, it is natural to expect that their properties are perturbed by their immediate environment.  This talk will focus on our different density functional theory works that highlight how the effects of the immediate environment determine the properties of 2D crystals.

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Christoph Boehme

DATE/TIME: Friday 11/19/2021; 2 PM (MST)

Location: Zoom Link

Short Biography:

A child of the 1970s, he was born and raised in Oppenau, a small town in southwest Germany, about 20 driving minutes east of the eastern French city of Strasbourg. After High School, obtaining an undergraduate degree in electrical engineering as well as 15 months of civil services caring for disabled people (chosen to avoid the military draft), he moved to Heidelberg, Germany in 1994 in order to study physics at the University of Heidelberg. He won a Fulbright Student Scholarship in 1997 which brought him to the US for the first time, where he lived in Raleigh, North Carolina and met his wife Kristie. In 2000 he and Kristie moved to Berlin, Germany where they lived for 5 years while he worked for the Hahn-Meitner Institut, a national laboratory. He finished his dissertation work as a graduate student of the University of Marburg in 2002 while still living and working in Berlin where he then also spent an additional three years after graduation to work as a postdoctoral researcher. He moved to Utah in 2006 to join the U's Department of Physics as an Assistant Professor. He was promoted into the rank of Associate Professor and awarded tenure in 2010, promoted to the rank of Professor in 2013 and he served as Associate Chair of the Department of Physics & Astronomy from July 2010 until August 2015. In 2019, he was appointed Physics & Astronomy Interim Department Chair.

Spin-based Quantum Sensing with Charge Carrier Spin States in Organic Semiconductors

Quantum sensors probe physical observables by utilizing the inherent volatility of quantum states due to interaction with their environment. Quantum sensors can overcome the sensitivity limits of classical sensors, and they can also probe inherently quantum mechanical observables such as entanglement and permutation symmetry; This presentation is about quantum sensing concepts based on electron spin states in organic condensed matter environments. Due to weak spin-orbit coupling, paramagnetic charge carrier states in π-conjugated polymer thin films are subject to pronounced spin selection rules and, also, they exhibit spin coherence times in the order of a s, limited only by unresolved proton hyperfine fields caused by the all-abundant hydrogen in these materials. The spin-selection rules enable straightforward electrical detection of coherent propagation of these spin states [1]. We have utilized these as spin-based quantum sensors [2] for the study of the non-perturbative drive regime of magnetic dipole excitations. These experiments have revealed previously not accessible magnetic resonant strong-drive phenomena, including spin-collectivity effects [3], multiple-quantum transitions occurring at integer and fractional g-factors, as well as a magnetic resonant Bloch-Siegert Shift [4,5].

[1] D.R. McCamey et al., Phys. Rev. Lett. 104 (1), 017601; [2] W. J. Baker et al., Nature Commun. 3, 898, (2012); [3] D. P. Waters et al., Nat. Phys., 11, 910 (2015); [4] S. Jamali et al., Nano Lett. 17, 4648 (2017); [5] S. Jamali et al., Nature Commun. 12 (1), 1 (2021).

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Dr. Mark C. Hersam

Northwestern University

DATE/TIME: 11/12/2021; 2pm MST

Location: Zoom Link 

Short Biography: 

Mark C. Hersam is the Walter P. Murphy Professor of Materials Science and Engineering and Director of the Materials Research Center at Northwestern University. He also holds faculty appointments in the Departments of Chemistry, Applied Physics, Medicine, and Electrical Engineering. He earned a B.S. in Electrical Engineering from the University of Illinois at Urbana-Champaign (UIUC) in 1996, M.Phil. in Physics from the University of Cambridge (UK) in 1997, and a Ph.D. in Electrical Engineering from UIUC in 2000. His research interests include nanomaterials, nanomanufacturing, nanoelectronics, scanning probe microscopy, renewable energy, and quantum information science. Dr. Hersam has received several honors including the Presidential Early Career Award for Scientists and Engineers, TMS Robert Lansing Hardy Award, AVS Peter Mark Award, MRS Outstanding Young Investigator, U.S. Science Envoy, MacArthur Fellowship, AVS Medard W. Welch Award, and eight Teacher of the Year Awards. Dr. Hersam has repeatedly been named a Clarivate Analytics Highly Cited Researcher with over 600 peer-reviewed publications that have been cited more than 50,000 times with an h-index of 109. An elected member of the National Academy of Inventors, Dr. Hersam has founded two companies, NanoIntegris and Volexion, which are commercial suppliers of nanoelectronic and battery materials, respectively. Dr. Hersam is a Fellow of MRS, ACS, AVS, APS, AAAS, SPIE, and IEEE, and also serves as an Associate Editor of ACS Nano.

Boron in the 2D Limit: Borophene, Borophane, and Beyond

The recent experimental realization of 2D boron (i.e., ‘borophene’) has spurred broad interest in its unique material attributes such as in-plane anisotropy, seamless phase intermixing, high mechanical strength and flexibility, massless Dirac fermions, and phonon-mediated superconductivity [1]. The polymorphic nature of borophene, which is rooted in the rich bonding configurations among boron atoms, further distinguishes it from other 2D materials and offers an additional means for tailoring its material properties [2]. This presentation will explore the ultrahigh vacuum synthesis and atomic-scale characterization of borophene on noble metal substrates including Ag(111) [3] and Au(111) [4]. In addition to distinct borophene polymorphs, conditions for forming self-assembled intermixed phases [5], superlattices [6], and bilayers [7] will be delineated. Using field emission resonance spectroscopy, the work function and degree of electron transfer doping can be quantified, revealing subtle differences between the different borophene phases [8]. By exploiting spatially inhomogeneous surface chemistry, seamless 2D heterointerfaces can also be realized between borophene and other materials including organic semiconductors [9], graphene [10], and graphene nanoribbons [11], each of which show atomically sharp electronic interfaces as confirmed by scanning tunneling microscopy and spectroscopy. In an effort to further tune the chemical and electronic properties of 2D boron, covalent hydrogenation of borophene has been achieved, resulting in a series of ‘borophane’ polymorphs that possess significantly higher stability in ambient conditions compared to pristine borophene [12]. Overall, this work establishes a series of design rules for manipulating and integrating 2D boron into a range of next-generation electronic [13] and quantum technologies [14].

[1] A. J. Mannix, et al., Nature Nanotechnology, 13, 444 (2018). [2] H. Bergeron, et al., Chemical Reviews, 121, 2713 (2021). [3] X. Liu, et al., Nature Communications, 10, 1642 (2019). [4] B. Kiraly, et al., ACS Nano, 13, 3816 (2019). [5] X. Liu, et al., Nature Materials, 17, 783 (2018). [6] L. Liu, et al., Nano Letters, 20, 1315 (2020). [7] X. Liu, et al., Nature Materials, DOI: 10.1038/s41563-021-01084-2 (2021). [8] X. Liu, et al., Nano Letters, 21, 1169 (2021). [9] X. Liu, et al., Science Advances, 3, e1602356 (2017). [10] X. Liu, et al., Science Advances, 5, eaax6444 (2019). [11] Q. Li, et al., Nano Letters, 21, 4029 (2021). [12] Q. Li, et al., Science, 371, 1143 (2021). [13] V. K. Sangwan and M. C. Hersam, Nature Nanotechnology, 15, 517 (2020). [14] X. Liu and M. C. Hersam, Nature Reviews Materials, 4, 669 (2019).

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Dr. Di Xiao

DATE/TIME: 11/05/2021; 2PM (MDT)

Location: Zoom Link

Short Biography:

Di Xiao obtained his Bachelor degree in physics from Peking University and PhD from the University of Texas at Austin.  After a four-year stint at Oak Ridge National Laboratory, he moved to Carnegie Mellon University in 2012.  He joined the University of Washington in 2021, and holds professor position in both Department of Physics and Department of Materials Science & Engineering.  Xiao is an expert in Berry phase effect, and pioneered the field of valleytronics.  He was named a Cottrell Scholar by Research Corporation for Science Advancement in 2016, Simons Fellows in Theoretical Physics in 2019, and has been a Thomson-Reuters Highly Cited Researcher since 2017.

Chiral Effect in Twisted Van der Waals Heterostructures

Recent years have seen a surge of interest in twisted van der Waals heterostructures consisting of atomically thin crystal layers. From a structural point of view, twisted layers are interesting because not only are they chiral, but their chirality can be readily controlled by varying the twisting angle. For example, bilayers with opposite twisting angles are mirror images of each other; therefore, they possess opposite chirality. This structural flexibility makes twisted van der Waals heterostructures a versatile platform for investigating chirality-dependent phenomena.  In this talk, I will discuss two phenomena related to the chirality of twisted bilayers, namely, chiral charge pumping and layer circular photogalvanic effect.  The former relates mechanical motion to electricity, while the latter could be useful for frequency-sensitive, circularly polarized light detection, particularly in the infrared range.

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Dr. TeYu Chien

University of Wyoming

DATE/TIME: Friday October 29, 2021 2PM MDT

Location: Zoom Link

Short Biography:

Chien received B.S. degree from National Taiwan Normal University in Physics in 2001 and Ph. D degree from University of Tennessee, Knoxville with thesis focus on the electron-phonon coupling on Be(0001) surface studied with Angle-Resolved PhotoEmission Spectroscopy (ARPES) in 2009. From 2009-2011, Chien worked as a postdoc focusing on developing cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S) technique for perovskite oxide interfaces in Center for Nanoscale Materials and Advanced Photon Source at Argonne National Laboratory. Chien continued his research as a second postdoc position at Northwestern University focusing on modifying graphene covalently and non-covalently aiming toward opening band gaps. Chien joined UW in 2013 and was promoted to Associate Professor in 2019. His research interests include electronic and magnetic properties of nanomaterials, topological materials, magnetic materials, renewable energy materials, and materials for quantum information science. He has won College of Arts & Sciences Extraordinary Merit in Research Award at University of Wyoming in 2018 and Thumbs Up Award from the College of Arts & Science Dean’s Undergraduate Council at University of Wyoming in 2020.

 

Electronic Properties of Novel Materials – Photovoltaic, 2D Magnetic, and Topological Materials

Electronic properties, such as the electronic band structures and the density of states, of a material are at the center of understanding the physical properties. The electronic properties are directly related to the optical, magnetic, and transport properties of the materials. Thus, the understanding of the electronic properties provides the fundamental basis of understanding the materials of interests. In this talk, I would like to share the results of our recent and on-going works focusing on three material categories: (1) photovoltaic materials (organic photovoltaic, and organometallic halide perovskite materials); (2) magnetic materials (CrBr3, Eu-Si nanowires, and EuO); and (3) topological materials (2M-WS2). Scanning tunneling microscopy and spectroscopy (STM/S) is the main tool used to provide the nm-scale understanding of the electronic properties in these materials. If time permits, I will also discuss the future directions.

 

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Dr. Steven Tomczyk

National Center for Atmospheric Research, Boulder, CO

DATE/TIME: Friday October 29, 2021  4PM MDT

Location: Physical Sciences 234

Short Biography:

Steven Tomczyk is a Senior Scientist at the High Altitude Observatory (HAO) of the National Center for Atmospheric Research (NCAR). Steve was born and raised in New Jersey. He received his BS degree from Villanova in 1979, and his PhD from UCLA in 1988, both in Astronomy. He has been at NCAR for his post-graduate career where he has been developing instruments for observing waves and magnetic fields in the solar atmosphere. His current focus is on instrumentation for the remote sensing of magnetic fields in the Sun’s corona. Steve is the principal investigator of the Coronal Solar Magnetism Observatory, a proposed facility dedicated to monitoring magnetic fields and plasma properties in the large-scale solar corona.

Measuring Magnetic Fields in the Solar Corona - Towards Understanding the Sources of Space Weather

The Sun influences the Earth due to its variable output of radiation, energetic particles, and magnetized plasma. Eruptive events on the Sun can drive radical disturbances in the near-Earth environment known as space weather. Many critical technologies upon which society has become increasingly dependent are vulnerable to the effects of space weather including satellites, communication networks, navigation systems and power grids. In addition, space weather events pose a hazard to humans in space and airline crews and passengers on polar routes.

The physical mechanisms at the Sun giving rise to space weather are poorly understood in detail. What is certain is that magnetism in the solar corona plays the central role in driving space weather events. While magnetism is well observed in the solar photosphere, it is not adequately measured in the solar corona due to the faintness of the corona compared to the solar disk (5 orders of magnitude)  and the weak strength of magnetic fields in the corona (~10 Gauss). Progress towards understanding the mechanisms that lead to space weather, and eventually predicting the occurrence of solar storms requires that we develop the ability to measure magnetic fields routinely in the corona.

In this talk, I will introduce the topic of space weather, and motivate the need to measure magnetic fields in the corona. I will describe the techniques we have at our disposal to remotely sense coronal magnetism. And I will describe the Coronal Solar Magnetism Observatory (COSMO), a project we are developing that has as its central element a 1.5-m aperture coronagraph. The COSMO project has been funded by NSF to perform a site survey to identify a location for the COSMO observatory and to work with a design firm to design the COSMO coronagraph.

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Yan (Sarah) Li

University of Utah

DATE/TIME: 10/22/2021; 2PM MST

Location: https://uwyo.zoom.us/j/95010441800

Short Biography:

Sarah Li received her PhD in physics at UC Riverside in 2010, and worked as Director’s postdoc Fellow at the National High Magnetic Field Lab at Los Alamos National Lab after that. She started her own research lab as an assistant professor at Department of Physics and Astronomy at University of Utah in 2013. Her group focuses on optical studies of spin dynamics and magnetism in semiconductors in bulk and low dimensions.

Spin Dynamics and Interplay with Carrier Dynamics in Lead Halide Perovskites

Lead halide perovskites are an emerging class of semiconductors, and remarkable progress has been made in photovoltaic and other optoelectronic applications in the last decade. While substantial research efforts are on solving practical issues impeding commercialization, many fundamental properties of the materials still need to be investigated in-depth to overcome current challenges and exploit their full potential for applications beyond optoelectronics. These materials hold great promise for spintronics, because of their large and tunable spin-orbit coupling, spin-dependent optical transitions, and potential easy spin manipulation. Previously we have demonstrated optical orientation of spin-polarized excitons and spin coherence in polycrystalline MAPbI3 films [1]. Two mysteries had arisen in our study -- long spin lifetime (> 1 ns) with the presence of large spin-orbit coupling, and extremely small exchange couplings of the excitons (< 1micro eV). In order to unravel the mysteries, we studied spin dynamics on high quality MAPbI3 single crystals with low defect density. Details of intrinsic spin dynamics are revealed in MAPbI3, which offers insights into the interplay between spin dynamics and carrier dynamics following photo excitation. In this talk, we will present our current understanding about the spin-polarized exciton states in magnetic field and spin relaxation mechanisms in prototype bulk lead halide perovskite materials. All the recent studies on spin-dependent properties suggest that the halide perovskites are promising platform materials for spintronics, and many more interesting phenomena are yet to be explored and incorporated into spin-based device applications.

[1] P. Odenthal et al., Nature Physics 13, 894 (2017)

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jianshi zhou

Dr. Jianshi Zhou

DATE/TIME: Friday Sept. 24, 2021;  2-3PM MDT

Location: Zoom Link

Short Biography: 

Dr Zhou obtained his Bachelor (82), Master (85), and Ph.D. (91) in Physics from Jilin University, China. He is currently a research professor in Mechanical Engineering, University of Texas at Austin. His research interests focus on magnetism, superconductivity, orbital physics, and metal-insulator transition in transition-metal oxides. Major approaches to obtain new materials in his laboratory include the crystal growth by the floating zone method, high-pressure synthesis, and spark plasma sintering.  

Ferroelectric Metals and Perspective

Almost all ferroelectrics are insulators. Ferroelectricity arises due to the long-range dipole-dipole interaction. Metallicity and ferroelectricity are seemingly incompatible since free electrons screen the dipole-dipole interaction. The transition to a polar phase is possible in a metal as long as free electrons do not interact strongly with the transverse optical phonons as postulated by Anderson and Blount (AB) in 1965. The ferroelectric metal defined by AB is distinguishable from the metals with breaking inversion symmetry. LiOsO3 discovered in recent years fulfills the requirement of a ferroelectric metal, but the origin for the ion displacement is different from the description given by AB. In this talk, I will give an overview of achievements on the ferroelectric metal in the literature and demonstrate the recent development, especially, the new results from my group. 

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Dr. Jiadong Zang

DATE/TIME: Friday 09/10/2021; 2-3 PM MDT

Location: Meeting Link 

Short Biography:

Prof. Zang received his bachelor degree in 2007 and PhD degree in 2012, both from Fudan University. He worked as a postdoctoral fellow in the Institute of Quantum Matter at the Johns Hopkins University from 2012-2015. In 2015, he joined both the Department of Physics and Materials Science Program at the University of New Hampshire as an Assistant Professor, and was promoted to Associate Professor in 2020. His research focuses on many aspects of magnetism, especially topological magnetism, quantum transport, functional magnetic materials and 3D tomography. His research has been continuously supported by Department of Energy. He is a recipient of 2020 IUPAP Young Scientist Medal in the field of magnetism, and an Alexander von Humboldt Fellow for Experienced Researchers.

Topological Spin Textures in Two-dimensions and Beyond

Chiral magnets are a series of magnets with broken inversion symmetry. A new type of spin interaction therein, the Dzyaloshinskii-Moriya interaction, stimulates the formation of many novel topological spin textures. One important example is the emergence of magnetic skyrmion, whose nontrivial topology enables unique dynamical property and thermal stability, and gives rise to promising applications in future spintronic devices.

A key transport signature of the skyrmion is the topological Hall effect, that is, the electron moves in sideway under the effect of real space Berry phase induced by spin chirality. In the first part of the talk, I will discuss how transport signatures can be used as footprint of skyrmions. On the other hand, I will also set an alarm that topological Hall effect should not be abused, since it could originated from momentum space Berry phase or atomic scale chirality from thermal fluctuations.

In the second part of the talk, I will generalize the skyrmion texture from two dimensions (2D) to three dimensions (3D), and discuss two relevant 3D spin textures in chiral magnets. One is the target skyrmion we recently observed, both theoretically and experimentally, in ultra-small nanodisks of chiral magnets. A target skyrmion consists of concentric helical rings and can be stabilized in the absence of external magnetic field. The other texture to be discussed is the magnetic hopfion. We propose the presence of zero-field hopfion in synthetic chiral magnetic multilayers. The transition from hopfion to the ground state, a monopole-antimonopole pair, can be fully understood as the topological transition between torus and sphere. These works could stimulate the development of 3D spintronics.

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Dr. Bharat Ratra

Kansas State University

Public Talk - Thursday 9/9/21 7PM Classroom Building 222

Astronomy Colloquium - Friday 9/10/21 4PM              Physical Sciences 234

Short Biography:

Bharat Ratra works in the areas of cosmology and astroparticle physics. Two of his current principal interests are developing models for the large-scale matter and radiation distributions in the universe and testing these models by comparing predictions to observational data.

In 1988, Ratra and Jim Peebles proposed the first dynamical dark energy model. Ratra was a National Science Foundation CAREER award winner in 1999. He was named a fellow of the American Physical Society in 2002 and a fellow of the American Association for the Advancement of Science in 2005. He received the 2012-2013 Commerce Bank Distinguished Graduate Faculty Award at Kansas State University.  He was awarded the 2017 Olin Petefish Award in Basic Sciences. 

Ratra joined Kansas State University in 1996 as an assistant professor of physics. He was a postdoctoral fellow at Princeton University, the California Institute of Technology and the Massachusetts Institute of Technology. Ratra earned a doctorate in physics from Stanford University and a master's degree from the Indian Institute of Technology in New Delhi.

9/9 7pm Thursday Public Talk:  The Accelerating Expanding Universe: Dark Matter, Dark Energy, and Einstein's Cosmological Constant

Dark energy is the leading candidate for the mechanism that is responsible for causing the cosmological expansion to accelerate. Bharat Ratra will describe the astronomical data which persuade cosmologists that (as yet undetected) dark energy and dark matter are by far the main components of the energy budget of the universe at the present time. He will review how these observations have led to the development of a quantitative "standard" model of cosmology that describes the evolution of the universe from an early epoch of inflation to the complex hierarchy of structure seen today. He will also discuss the basic physics, and the history of ideas, on which this model is based.

9/10 4pm Friday Astronomy Colloquium: The "Standard" Model of Cosmology ... and Open Questions

Experiments and observations over the last two decades have provided strong support for a "standard" model of cosmology that describes the evolution of the universe from an early epoch of inflation to the complex hierarchy of structure seen today. I review the basic physics, astronomy, and history of ideas, on which this model is based. I describe the data which persuade cosmologists that (as yet not directly detected) dark energy and dark matter are by far the main components of the energy budget of the universe. I conclude with a list of open cosmological questions.

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Dr. Chris Sneden

University of Texas at Austin

DATE/TIME: 04/30/2021  3 PM MDT

Location: Meeting Link

Short Biography

Education: Haverford College, BA, Astronomy, 1969
                University of Texas, PhD, Astronomy, 1973

Jobs: Indiana U, postdoc, 1973-74
        U California, Santa Cruz, Lecturer, 1974-75
        U Wyoming, Asst Prof, 1975-78
        U Washington, Lecturer, 1978-79
        U Texas, Faculty, 1979-present;
        Currently Rex G Baker Centennial Research Prof, Emeritus

Societies: Am Ast Soc, Int Ast Union, Ast Soc Pacific

Service: Astronomy Department Chair, 1998-2002
             Astrophysical Journal, Scientific Editor, 1996-2002
             Astrophysical Journal Letters Editor, 2002-2012
             Am Ast Soc Publications Committee, 2016-present                                                                         Hobby-Eberly Telescope Dark Energy Experiment,
             Publications Manager, 2019-present

Research Areas: Spectroscopy of unevolved and aging stars
                        Nucleosynthesis of the elements
                        Chemical evolution of the Galaxy
                        Globular and open star clusters
                        Near-infrared high-resolution spectroscopy
                        RR Lyrae variable stars
                        Atomic and molecular transition data

High-Resolution Infrared Spectroscopy: An Opening Window for Galactic Chemical Evolution Research

Describing the birth and evolution of the Milky Way Galaxy is a fundamental goal of modern astrophysics.  A prime observational tool in this endeavor is high-resolution stellar spectroscopy, from which detailed chemical compositions can lead to the nucleosynthetic history of our Galaxy.  For half a century high-resolution spectroscopy was limited to the optical window, (0.3-1 micron), but advances of the last couple of decades in telescope/instrument/detector design has opened up the infrared to detailed  chemical composition research.  In this talk I will concentrate on two innovative instruments developed at McDonald Observatory, which have led to complete spectral coverage in atmospheric-transparent 0.8 to 2.4 micron wavelength areas.  This IR spectral domain is crucial for investigations in dust-obscured regions of our galaxy.  I will concentrate on three important observational questions:  (1) Do IR and optical chemical composition results agree?  (2) What unique spectral features bring value-added information in the IR?  (3) What are the most important Galactic large-sample studies to undertake now, and in the future with 30m-class telescopes?

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Deep Jariwala

Dr. Deep Jariwala

University of Pennsylvania

DATE/TIME: 04/30/2021  2-3 PM MDT

Location: Meeting Link

Short Biography: 

Deep Jariwala is an Assistant Professor in Department of Electrical and Systems Engineering at the University of Pennsylvania (Penn). His research interests broadly lie at the intersection of new materials, surface science and solid-state devices for opto-electronics and energy harvesting applications.  Deep completed his undergraduate degree in Metallurgical Engineering from the Indian Institute of Technology, BHU in 2010. Deep did his Ph.D. in Materials Science and Engineering at Northwestern University graduating in 2015. Deep was a Resnick Prize Postdoctoral Fellow at Caltech from 2015-2017 before joining Penn in 2018 and starting his own group.  https://scholar.google.com/citations?user=u1CHA2sAAAAJ&hl=en

https://jariwala.seas.upenn.edu/

Low-Dimensional Materials for Advanced Logic, Memory and Photonics

The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. While a tremendous amount of research activity has occurred in assembling disparate 2D materials into “all-2D” van der Waals heterostructures and making outstanding progress on fundamental studies, practical applications of 2D materials will require a broader integration strategy. I will present our ongoing and recent work on integration of 2D materials with 3D electronic materials to realize logic switches and memory devices with novel functionality that can potentially augment the performance and functionality of Silicon technology. First, I will present our recent work on gate-tunable diode1 and tunnel junction devices based on integration of 2D chalcogenides with Si and GaN. Following this I will present our recent work on non-volatile memories based on Ferroelectric Field Effect Transistors (FE-FETs) made using a heterostructure of MoS2/AlScN2 and I also will present our work on Ferroelectric Tunnel Junction (FTJ) devices3 also based on thin AlScN. 

   Next, I will present our work on light-trapping in 2D chalcogenides and halide perovskites. I will present the effect of nano-structuring on hybridization between excitons, plasmons and cavity photons.4 I will extend this concept to 2D halide perovskites5 and demonstration of hybrid exciton-polariton emission at room temperatures. If time permits I will also give a brief overview on other ongoing efforts in the lab including tunable 1D optical materials,6 in-situ electron-microscopy7, 8 and scanning probe microscopy efforts.9 I will end by giving a broad perspective on future opportunities of 2D and other low-dimensional materials in basic science and applied microelectronics technology.

  1. Miao, J.; Liu, X.; Jo, K.; He, K.; Saxena, R.; Song, B.; Zhang, H.; He, J.; Han, M.-G.; Hu, W.; Jariwala, D. Nano Letters 2020, 20, (4), 2907-2915.
    2. Liu, X.; Wang, D.; Zheng, J.; Musavigharavi, P.; Miao, J.; Stach, E. A.; Olsson III, R. H.; Jariwala, D. arXiv preprint arXiv:2010.12062 2020.
    3. Liu, X.; Zheng, J.; Wang, D.; Musavigharavi, P.; Stach, E. A.; Olsson III, R.; Jariwala, D. arXiv preprint arXiv:2012.10019 2020.
    4. Zhang, H.; Abhiraman, B.; Zhang, Q.; Miao, J.; Jo, K.; Roccasecca, S.; Knight, M. W.; Davoyan, A. R.; Jariwala, D. Nature Communications 2020, 11, (1), 3552.
    5. Song, B.; Hou, J.; Wang, H.; Sidhik, S.; Miao, J.; Gu, H.; Zhang, H.; Liu, S.; Fakhraai, Z.; Even, J.; Blancon, J.-C.; Mohite, A. D.; Jariwala, D. ACS Materials Letters 2021, 3, (1), 148-159.
    6. Song, B.; Liu, F.; Wang, H.; Miao, J.; Chen, Y.; Kumar, P.; Zhang, H.; Liu, X.; Gu, H.; Stach, E. A.; Liang, X.; Liu, S.; Fakhraai, Z.; Jariwala, D. ACS Photonics 2020, 7, (10), 2896-2905.
    7. Han, M.-G.; Garlow, J. A.; Liu, Y.; Zhang, H.; Li, J.; DiMarzio, D.; Knight, M. W.; Petrovic, C.; Jariwala, D.; Zhu, Y. Nano Letters 2019, 19, 7859-7865.
    8. Kumar, P.; Horwath, J. P.; Foucher, A. C.; Price, C. C.; Acero, N.; Shenoy, V. B.; Stach, E. A.; Jariwala, D. npj 2D Materials and Applications 2020, 4, (1), 1-10.                                                                            9. Moore, D.; Jo, K.; Nguyen, C.; Lou, J.; Muratore, C.; Jariwala, D.; Glavin, N. R. npj 2D Materials and Applications 2020, 4, (1), 44.

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Dr. Daniel George

JP Morgan Chase

DATE/TIME: 04/23/2021; 4PM MDT

Location: Meeting Link

Short Biography: 

Daniel is a Vice President, Applied AI Lead at JPMorgan Chase specializing in time-series signal processing with deep learning. Previously, he was an AI Research Scientist at Google X. He completed his PhD in Astronomy, with a fellowship in Computational Science and Engineering, at the University of Illinois at Urbana-Champaign in 2018 and his Bachelor's degree in Engineering Physics with Honors from IIT Bombay in 2015. 

At NCSA, he pioneered the application of deep learning in gravitational wave signal processing for LIGO. He also worked on HPC at Los Alamos National Laboratory and on deep learning/NLP at Wolfram Research. He has won the ACM Student Research Competition, the LSST Data Science Fellowship, and the NVIDIA Fellowship. His long-term interests lie in applying cutting-edge computer science and technology, especially AI, to accelerate scientific discoveries.

Life after Astronomy PhD; From Silicon Valley to Wall Street

I will talk about my PhD research on deep learning for gravitational wave astronomy at UIUC, and my experiences afterwards working on moonshots at Google X and on machine learning for finance at JPMorgan Chase. I will discuss opportunities and suggestions for students interested in data science/machine learning roles and also highlight differences between academia, tech industry, and finance. Following the talk, there will be an extended Q&A session where questions on any topic are welcome.

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Dr. Rodrigo Nemmen

Universidade de Sao Paulo

DATE/TIME: 04/16/2021; 3PM MDT

Location: Meeting Link

Short Biography:

I am an astrophysicist and my goal is to understand black holes and their impact on the universe. My group works at the interface between theory and observations, quantifying how black holes interact with their surroundings, accreting matter, releasing radiation and accelerating particles into relativistic outflows which regulate the growth of their host galaxies. We are analysing a wide-range of multiwavelength observations of galactic nuclei—in particular gamma-rays—and using state-of-the-art numerical simulations of black hole accretion.

Black hole simulations with AI: Do androids dream of electric black holes?

Black holes accrete gas from their surroundings in a chaotic, turbulent manner. This colloquium will describe the pilot application of deep learning for black hole weather forecasting. Early results indicate that black hole simulations can benefit tremendously from AI. Along the way, I will explain the difference between artificial intelligence (AI), machine learning, and deep learning and why the scientific community is so excited about the latter.

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Dr. Zhiqiang Mao

Pennsylvania State University

DATE/TIME: 04/16/2021; 2-3 PM MDT

Location: Meeting Link

Short Biography:

Zhiqiang Mao is a professor at the Department of Physics of Pennsylvania State University. He received his PhD degree from the University of Science and Technology of China and completed his postdoctoral training at Kyoto University and Pennsylvania State University. He joined Tulane University as a faculty member in 2002 and worked there until 2018. He returned to Penn State in 2018 as a professor. His research interests include topological materials, 2D materials, correlated oxides and unconventional superconductors. He has published 365 papers in peer reviewed journals with an h-citation index of 57. He is also an elected APS fellow.

Novel Layered Magnetic Topological Materials

The combination of magnetism and non-trivial band topology can generate various topological quantum states, such as quantum anomalous insulators, axion insulators and Weyl semimetals. Searching for magnetic topological materials and understanding their underlying physics have been a focused research direction in recent years. In this talk, I will first give a brief introduction to this research area and then talk about our recent studies on two classes of magnetic topological materials: 1) intrinsic magnetic topological insulators (MnBi2Te4)(Bi2Te3)m (m=0, 1 & 2); 2) antiferromagnetic (AFM) Dirac semimetal (Sr/Ba)MnSb2. For the (MnBi2Te4)(Bi2Te3)m system, we have synthesized not only AFM but also ferromagnetic (FM) phases, which provides rich opportunities for observing novel magnetic topological phases. Through chemical potential tuning by Sb substitution for Bi, we have observed transport evidence of a long-sought topological state - an ideal type-II FM Weyl state with one pair of Weyl nodes [1, 2]. In (Sr/Ba)MnSb2, we not only observed the interaction between Dirac fermions and magnetism [3], but also discovered a novel Dirac state featuring spin-valley locking and bulk quantum Hall effect [4].

References:

[1] Lee et al., Phys. Rev. Research 1, 012011(R) (2019).

[2] Lee et al., arXiv:2002.10683.

[3] Liu et al., Nature Materials 16, 905 (2017).

[4] Liu et al., arXiv:1907.06318 (2019).

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Dr. Jak Chakhalian

Rutgers University

DATE/TIME: 04/09/2021; 2-3 PM

Location: Meeting Link

Short Biography:

Jak graduated from the University for British Columbia, Vancouver working on geometrically frustrated magnetism and high Tc superconductivity with muon spin spectroscopies (muSR). He continued his postdoctoral work at the Max Planck Institute for Solid State Research at Stuttgart, Germany. At MPI, Jak concentrated on the growth and soft x-ray spectroscopy of strongly correlated complex oxides thin films and superlattices, with emphasis on the interfaces between high Tc cuprates and CMR manganites. In 2006 he joined the University of Arkansas at Fayetteville, and in 2016 moved to  Rutgers, where he is Cloud Lovelace professor of physics and co-director of the center for Quantum Materials Synthesis (cQMS). Jak is one of the pioneers of the physics and synthesis of interfaces between strongly correlated quantum materials.

Emergent Topological Phenomena in Oriented Thin Films of Pyrochlore Iridates

The recent progress in synthesizing and discovering states and phenomena beyond the Landau symmetry-breaking paradigm in quantum materials has been quite extraordinary. These new modalities confront our views of fermions and bosons’ possible behavior in solids, yet in bulk remain frequently concealed from the modern experimental probes. To exacerbate, though by now topological phases are well-known for non-correlated compounds, they are scarcely found in correlated electron systems. In my talk, I will discuss a way of addressing these two challenges by creating new synthetic templates with rich many-body behavior derived from the rare-earth pyrochlore iridates and (ii) discovering quantum states and phenomena entwined with spin correlations and non-trivial band topology.

Specifically, I will focus on quantum states of (111)-oriented rare-earth iridium pyrochlore thin-films La2Ir2O7 (La = Pr ... Lu) which is (1) a model system for an exotic nodal non-Fermi liquid metal known as the Luttinger-Abrikosov-Beneslavskii state, and (2) time-reversal broken Weyl semimetal. During the talk, I will discuss the challenges of growing complex materials of platinum group metal oxides and finding direct signatures for the presence of Weyl fermions.

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Dr. Gary Cheng

Purdue University

DATE/TIME: 03/26/2021; 2-3 PM

Location: Meeting Link

Short Biography:

Prof. Gary Cheng holds his Ph.D. in mechanical engineering from Columbia University (2002).  He is a professor in School of Industrial Engineering and School of Materials Engineering in Purdue University and an ASME fellow.  His research and teaching interests include laser materials processing, mechanical behaviors, nanolithography, additive manufacturing, electrical and optical properties, metamaterials. He has published more than 180 articles in journals including Science, Advanced Materials, Nature Communication, Matter, Materials Today, NanoToday, Nano Letters, ACS Nano, etc. His research was highlighted in Nature Photonic, Nature Research Materials, NanoToday.  He has 13 US awarded patents and provisional applications.  He has been recognized by NSF CAREER Award, ONR Young Investigator Award, SME outstanding young manufacturing engineer, ASME Cho & Trigger Young Investigator Award, National Research Council senior research fellowship, University Faculty Scholar Award, ASME best papers, Purdue Innovator Hall of Fame.

Laser Shock Nano-Straining in 2D Materials

Straining nanomaterials to break their lattice symmetry is perhaps the most efficient approach toward realizing bandgap tunability.  Graphene has a great potential to replace silicon in prospective semiconductor industries due to its outstanding electronic and transport properties; nonetheless, its lack of energy bandgap is a substantial limitation for practical applications. In this talk, a large-scale strain engineering technique to control the local strains in 2D materials and their heterostructures will be discussed. First, laser shock nanostraining will be introduced to generate three-dimensional (3D) nanostructures and thus induce local strains in the graphene sheet. The size dependent straining limit of the graphene and the critical breaking pressure will be discussed.  Moreover, laser shock nanostraining induces modulated inhomogeneous local asymmetric elastic–plastic strains as results of 1-100 GPa‐level shock loading at a high strain rate of 106–108 s−1. Currently, due to the weak lattice deformation induced by uniaxial or in‐plane shear strain, most strained graphene studies have yielded bandgaps <0.5 eV, laser shock nanostraining can induce tunable bandgaps in graphene of up to 2.1 eV.  Finally, laser shock nanostraining will be discussed to controllably tune the interlayer distance between VdW heterostructures and generate strain coupling between layers.  The strains in the 2D heterolayers, providing a simple and effective way to modify their optic and electronic properties.

 

  1. Link to References

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Dr. Craig Wheeler

DATE/TIME: 3/26/21; 3PM MDT

Location: Meeting Link

Short Biography:

Craig Wheeler is the Samuel T. and Fern Yanagisawa Regents Professor of Astronomy, Emeritus, and Distinguished Teaching Professor, Emeritus, at the University of Texas at Austin, and past Chair of the Department. He is a Fellow of the American Physical Society and a Legacy Fellow of the American Astronomical Society. He has published nearly 400 refereed scientific papers, as many meeting proceedings, a professional-level book on supernovae (Supernova Explosions), a popular book on supernovae, gamma-ray bursts and related topics (Cosmic Catastrophes), two novels (The Krone Experiment and Krone Ascending), and has edited six books. Wheeler has received many awards for his teaching, including the Regents Award, and is a popular science lecturer.  He was a visiting fellow at the Joint Institute for Laboratory Astrophysics (JILA), the Japan Society for the Promotion of Science, the Cerro Tololo Interamerican Observatory, and a Fulbright Fellow in Italy.  He has served on a number of agency advisory committees, including those for the National Science Foundation, the National Aeronautics and Space Administration, and the National Research Council.  He has held many positions in the American Astronomical Society and was President of the Society from 2006 to 2008.  His research interests include supernovae, black holes, astrobiology, high energy density astrophysics, and the technological future of humanity. 

Betelgeuse: Active Now, Doomed to Explode Later

Betelgeuse is in many ways a typical massive red giant star doomed to explode when its core burns out and collapses to form a neutron star. It is also special because it is close enough at 500 light years to be spatially resolved and hence studied in unprecedented detail. The Great Dimming of early 2019 has only added to its allure. Some years ago, I began work with a group of undergraduates, the initial goal of which was to try to better estimate when Betelgeuse might explode. Our first discovery was that a single-star picture failed drastically to accounting for  the  observed  rotational  velocity.  The  rotation  would  be  much  too slow. We proposed that Betelgeuse was originally a binary system that underwent a merger to form a single more rapidly rotating star. I will summarize recent work that has elucidated the nature of Betelgeuse and its Great Dimming.

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Dr. Ben Boizelle

DATE/TIME: 03/19/2021; 4-5 PM

Location: Meeting Link

Short Biography: 

After graduating from Brigham Young University – Provo with a BS in Physics & Astronomy in 2012, Benjamin Boizelle pursued graduate studies at the University of California, Irvine, earning MS and PhD degrees in Physics and Astronomy. During these years, he also taught introductory astronomy courses at nearby Santa Ana College. In 2018, he began working with Professor Jonelle Walsh at Texas A&M University as a postdoctoral researcher. In 2020, he began as an assistant professor at Brigham Young University. In addition to black holes, Dr. Boizelle's research interests include active galaxies, dust attenuation, and transient astronomical phenomena.

Wrangling the Beast – Precision Supermassive Black Hole Mass Measurement With ALMA

While supermassive black holes (BHs) gravitationally dominate only the innermost regions of galaxies, their masses correlate with large-scale galaxy properties, hinting that BHs co-evolve with their host galaxies over the age of the universe. These correlations suggest a distinct evolutionary pathway for the most luminous galaxies; however, an incomplete census of >10^9 solar mass BHs (and large measurement uncertainties) preclude any definitive conclusions. Emission-line observations with the Atacama Large Millimeter/submillimeter Array (ALMA) are opening a new avenue for studying BH demographics in nearby galaxies. I will present ongoing ALMA CO imaging that has resolved circularly-rotating molecular gas disks in the nuclei of a growing number of very luminous galaxies, providing ideal probes of their inner gravitational potentials. I will highlight results from recent gas-dynamical modeling efforts, which have enabled some of the most precise direct BH mass determinations to date and important cross-checks with other measurement techniques. I will also discuss the prospect of future telescopes like the next-generation Very Large Array (ngVLA) to expand on ALMA's revolutionary capabilities.

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kin fai mak headshot

Dr. Kin Fai Mak

Cornell University

DATE/TIME: 03/19/2021; 2-3 PM 

Location: Meeting Link

Short Biography:

I received my PhD in physics from Columbia University working with Prof. Tony Heinz on optical spectroscopy of 2D materials such as graphene and MoS2. As a postdoc, I worked with Prof. Paul McEuen and Prof. Jiwoong Park at Cornell on the optoelectronic properties of 2D semiconductors. We have demonstrated the valley Hall effect in MoS2 transistors using optoelectronics methods. I started my faculty position at Penn State University in 2014 and moved back to Cornell in 2018. I am now an associate professor of physics and of applied and engineering physics. I am interested in many topics in condensed matter physics. My current research interests include magnetism, superconductivity, strong correlation physics and exciton physics in 2D materials and their heterostructures.  

Hubbard Model Simulation in Moiré Materials

The Hubbard model is a simple theoretical model of interacting quantum particles in a lattice. It is thought to capture the essential physics of high-temperature superconductors and other complex quantum many-body phenomena, but has proved difficult to solve accurately. Physical realizations of the Hubbard model therefore have a vital role to play in solving the strong-correlation puzzle. Moiré materials, metamaterials built on artificial “moiré atoms”, have recently emerged as a promising Hubbard model simulator. The ability to continuously control the Hubbard Hamiltonian in these materials has provided a unique opportunity to address some of the long-standing questions in condensed matter physics. For instance, can unconventional superconductivity and quantum spin liquids emerge from the Hubbard model? In this talk, I will discuss recent efforts to simulate Hubbard model physics in moiré materials. Specific examples on realizing the Mott insulating state, the Mott-Hubbard transition and electron crystals will be discussed. I will end with a brief discussion on opportunities and challenges for future studies.

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Jin Hu

Dr. Jin Hu

University of Arkansas

DATE/TIME: 03/12/2021  2-3 PM MST

Location: Zoom Meeting Link

Short Biography:

Jin Hu is an assistant professor of physics at the University of Arkansas. He received BS degree from University of Science and Technology of China in 2008 and PhD degree from Tulane University in 2013. He also did his postdoctoral training at Tulane and became a research assistant professor there, before joining University of Arkansas in 2017.

His research focuses on various quantum material systems including unconventional superconductors, topological materials, and 2D materials. He has published 89 papers since 2009, with a total citation around 4200 and H-index of 33.

Advanced Materials for Condensed Matter Physics

The advance of condensed matter physics has been promoted by the discoveries of novel quantum materials. The recent examples include novel functional 2D materials and topological semimetals. In this talk, I will introduce a few advanced functional materials, including functional 1D semiconductors, 2D materials, and the emerging topological semimetals. The studies of these materials lead to the discovery of new physics concepts and technological useful properties.

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Helin Cao photo

 

Dr. Helin Cao

Intel Corporation

DATE/TIME: 03/05/2021  12-1 PM

Location: Meeting Link

 

Short Biography:

Helin received his Ph.D. in Physics from Purdue University, where he focused on electronic properties on topologically and geometrically non-trivial materials. After 1 year of postdoctoral research at another UW (University of Washington), Helin joined Intel. During 6 years at Intel, he switched roles between device engineer, AI software architect, and product marketing to maximize his industrial experiences. Helin published 25 research papers and filed 3 patents. 

10x Rule that Drives Innovations in Academic and Industrial Research

Peter Theil, Paypal’s co-founder, wrote in his book Zero to One: “As a good rule of thumb, proprietary technology must be at least 10 times better than its closest substitute in some important dimension to lead to a real monopolistic advantage.” He suggests that only when a startup has something exponentially better than its competition, its success can be foreseen. While reflecting on my own experiences in conducting research, I find the “10x rule” also applies to academic activities. In this talk, I will share several examples that validate the rule, and discuss how to use it as a framework to think through the value of a research.

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Yuri Dahnovsky

Dr. Yuri Dahnovsky

Department of Physics and Astronomy, University of Wyoming

DATE/TIME: 2/5/2021   2-3pm MST

Location: Zoom Meeting Link

Short Biography:

Yuri Dahnovsky finished the Department of Chemical and Molecular at Moscow Institute of Physics and Technology (Moscow, USSR) in 1974. He defended his Ph. D. in Theoretical Physics at the Institute of Chemical Physics of the USSR Academy of Sciences in Moscow in 1981. In 1992 – 1998 Yuri worked as a research associate at the University of California at Santa Barbara, Carnegie-Mellon University, University of Pittsburgh, and North Western University in the US. In 1998 Yuri joined the Physics department at UW where he works now.

Yuri’s area of expertise is rather broad. He studied electron transfer in polar media., instanton tunneling, tunneling with dissipation, electron tunneling in a strong time-dependent electric field. At UW Yuri studied electrical properties in molecular wire based on nonequilibrium Green’s functions. Then his main interest was mainly in quantum dot solar cells. For this project Yuri has developed the rather general approach based on nonequilibrium Green’s functions. Yuri interest in magnetism was initially in quantum dot materials (d0 ferromagnetism). He was also interested in microporous materials that can be useful for drug delivery. Recently he studies quantum materials, in particular spin-dependent Hall effect with conduction electrons scattered by skyrmions. Yuri has published about 140 research articles and four books.

Electron Tunneling Driven by a Time-Dependent Electric Field

This talk is about of electron tunneling driven by a strong time-dependent field. First, we discuss tunneling quantum transfer with dissipation introduced by Anthony Leggett. Quantum dissipation will be presented by a harmonic bath interacting with a particle. We also discuss the concept of coherent and incoherent tunneling. We introduce a two-level system interaction with an oscillator environment as the simplest model of a tunneling system. Then we discuss the electron tunneling in a time-dependent monochromatic electric field. In particular, we consider coherent and incoherent tunneling in a time-dependent electric field. Then we discuss the electron tunneling in a pulsed cw field where induced coherent oscillation can take place despite the strong dissipation. There are many interesting features of electron tunneling in a bichromatic electromagnetic field, which are discussed in the presentation. We apply the concepts of electron tunneling driven by a time-dependent electric filed to electron transfer in quantum well using the Bardeen’s Hamiltonian. We find the system can exhibit the effect of absolute negative resistance, i.e., the electron moves to the opposite direction. Finally, we discuss light absorption accompanied the electron transfer in a time-dependent field. The problem under consideration is solved by the methods that does not consider the perturbation theory. In this problem the absorption peak positions depend on the light intensity.

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