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Upcoming Colloquia

Department of Physics & Astronomy                                                                                  Colloquia Archive

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Yan Li  headshot

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. Zang headshot

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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zhiquiang mao photo

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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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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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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