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Upcoming Colloquia

Department of Physics & Astronomy                                                                                  Colloquia Archive

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rob goldston

Prof. Rob Goldston

Date: 09/25/2020

Time: 2:00-3:00 PM

Discussion Section: 3:00-4:00PM

Location: ZOOM (link to meeting)

 

Short Biography:


Rob Goldston is a professor of Astrophysical Sciences at Princeton University and associated faculty with Princeton’s Program on Science and Global Security. His research interests include neutron-based methods to verify warheads for disarmament, non-invasive UF6 flow meters and neutron detectors to verify operation of gas-centrifuge enrichment plants, and robotic techniques to monitor areas for undeclared nuclear materials and activities. He serves on the Board of the Council for a Livable World and writes policy pieces for the Bulletin of the Atomic Scientists.

The New Nuclear Arms Race, Its Dangers, and How to Turn it Around



Abstract: The United States and Russia are engaged in the first phases of a new nuclear arms race. With the recent shredding of arms-control agreements, this race may proceed unfettered and could lead to unprecedented dangers to humanity. As scientists we are obliged to understand the dynamics of this race and its dangers, and to lead in averting the rush to oblivion.

 

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albert rigosi

Dr. Albert F. Rigosi

 

Date:10/02/2020

Time: 2:00 PM

Location: Zoom (link to meeting)

 

Short Biography:

 

Dr. Rigosi received the B.A., M.A., M.Phil., and Ph.D. degrees in physics from Columbia University, New York, NY. From 2008 to 2015, he was a Research Assistant with the Columbia Nano Initiative. From 2015 to 2016, he was a Joint Visiting Research Scholar with the Department of Applied Physics of Stanford University in Stanford, CA, and the PULSE Institute of SLAC National Accelerator Laboratory in Menlo Park, CA. Since 2016, he has been a Physicist at the National Institute of Standards and Technology in Gaithersburg, MD. His research interests include two-dimensional electron systems and applications of those systems’ behaviors for electrical metrology.

Applications of Graphene Quantum Hall Devices for Defining the Ohm

Did you know that the United States recently became the first nation to use graphene in how the unit of the ohm is defined? Monolayer epitaxial graphene has been shown to have clearly superior properties for the improvement of devices (called QHRs) whose function depend on the quantum Hall effect and serve a critical role in defining electrical units for US industries. The recent progress in the development of these devices will be summarized in this talk, with specific focus on the following topics:
(1) Stabilizing and controlling graphene’s electron density over centimeter scales without the use of electrostatic gating.
(2) Expanding the utility of these graphene-based QHR devices by creating arrays that employ superconducting electrical contacts.
(3) Exploring the avenue of p-n junctions as a possible future device to access many different quantum Hall resistance values.

 

 

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kyle dawson

Kyle Dawson

Date: 10/02/2020

Time: 4:00pm

Location: Zoom (link to meeting)


Short Biography:

 Prof. Kyle Dawson joined the University of Utah faculty in 2009 after spending nine years in Berkeley as a graduate student and Postdoctoral Researcher. He was the Principal Investigator for the Extended Baryon Oscillation Spectroscopic Survey, the program within the Sloan Digital Sky Survey to constrain cosmology through the clustering of matter on scales of hundreds of millions of lightyears. Prof. Dawson is now the co-Spokesperson for the Dark Energy Spectroscopic Instrument (DESI). DESI will be the largest spectroscopic survey ever conducted, designed to map the cosmic distance scale and growth of structure over the last 12 billion years.

In July, 2020, eBOSS released the final measurements and cosmological interpretation of those measurements. These results will be the topic of the October 2 colloquium.

Final BAO and RSD Measurements

The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) concluded observations of the cosmic distance scale and the growth of structure in February, 2019. The three dimensional clustering in all samples from the Sloan Digital Sky Survey (SDSS) was used to make 15 distinct, high precision measurements of Baryon Acoustic Oscillations (BAO) to an effective redshift z<2.4 and six measurements of redshift space distortions (RSD) to z<1.5. With this redshift coverage and sensitivity, the SDSS experiment is unparalleled in its ability to explore models of dark energy. Using available cosmological samples, we provide new constraints on the cosmological model with an emphasis on the role of the final BAO and RSD clustering measurements in advancing the cosmological model. In this talk, I will give a brief overview of the BAO and RSD measurements and present the highlights of the advances in modeling dark energy, the local expansion rate, tests of general relativity, neutrino masses, and the overall cosmological model.

For those who would like an introduction before the presentation, please visit the eBOSS Results webpages:
Final BAO and RSD Measurements
Cosmology Results from eBOSS

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Cheng Gong

Dr. Cheng Gong

Date: 10/09/2020

Time: 2:00PM - 3:00 PM

Location: Zoom (link to meeting)

 Short Biography:

Dr. Cheng Gong is an assistant professor in the Department of Electrical & Computer Engineering and Quantum Technology Center (QTC) at the University of Maryland, College Park. Dr. Gong is a recipient of IUPAP Young Scientist Prize in Semiconductor Physics 2020. His group focuses on magnetic, electronic and optical properties of 2D materials, nanostructures and nanodevices, studied by a variety of optical and electrical approaches in synergy with density functional theory calculations. From 2014 to 2019, he was a postdoctoral fellow at University of California, Berkeley, where he pioneered the discovery of the first magnetic 2D material and innovated the development of spintronic devices based on magnetic 2D materials and heterostructures. He received his Ph.D. in 2013 in Materials Science and Engineering at the University of Texas at Dallas.

 

 

2D Magnets and 2D Magnetism

 

Magnetism, one of the most fundamental physical properties, has revolutionized significant technologies such as data storage and biomedical imaging, and continues to bring forth new phenomena in emerging materials of reduced dimensionalities. The recently discovered magnetic 2D van der Waals materials provide ideal platforms to enable the atomic-thin, flexible, lightweight magneto-optical and magnetoelectric devices. Though many have hoped that the ultra-thinness of 2D magnets should allow an efficient electrical control of magnetism, the state-of-the-art has not achieved notable breakthroughs to this end. In this talk, I will speak on our experimental discovery of the first 2D ferromagnet, analyze the current progress and existing challenges in this emerging field, and propose promising strategies towards the efficient electrical control of 2D magnetism for low-power spintronics.

 

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hugh churchill

Dr. Hugh Churchill

Date: 10/16/2020

Time: 2-3 PM

Location: ZOOM (link to meeting)

Short Biography:

Hugh Churchill is an assistant professor of Physics at the University of Arkansas. He received a Ph.D. in Physics from Harvard University in 2012, and before joining UA in 2015, he held a Pappalardo Fellowship at the Massachusetts Institute of Technology. Churchill’s work encompasses a variety of electronic, optical, and topological properties of low-dimensional systems including Ge/Si and InSb nanowires, carbon nanotubes, and 2D semiconductors. At UA, the Churchill Lab combines expertise in nanofabrication with quantum transport and optoelectronic characterization to investigate the electronic, magnetic, and optical properties of atomically thin 1D and 2D semiconductor quantum devices. Current research interests include qubits based on spin and valley degrees of freedom as well as unconventional magnetic, topological, and optoelectronic properties of layered materials. Churchill is a recipient of early career awards from NSF and AFOSR, including the PECASE in 2019.

Quantum Devices with 2D Semiconductors and Insulators

In this talk I will describe two applications of 2D layered materials for quantum devices. First, I will discuss our work to fabricate and characterize gate-defined, accumulation mode quantum dots using monolayer and bilayer WSe2. The devices are operated with gates above and below the WSe2 layer to accumulate a hole gas, which for some devices is then selectively depleted to define the dot. Temperature dependence of conductance in the Coulomb-blockade regime is consistent with transport through a single level, and excited-state transport through the dots is observed at temperatures up to 10 K. These devices provide a platform to evaluate valley-spin states in monolayer and bilayer WSe2 for application as qubits. Second, I will discuss gate-tunable Josephson junction field-effect transistors (JJ-FETs) based on Al/InAs in which the gate dielectric is thin hBN. Comparing devices with hBN and AlOx dielectrics, we observe that the product of normal resistance and critical current, IcRn, is comparable for both types of devices. However, Rn is strikingly higher for the hBN-based devices indicating that the surface is doped less compared to AlOx gate dielectric. These results demonstrate that hBN provides a superior gate dielectric compared to AlOx for JJ-FET devices with applications in superconducting logic and quantum information technologies such as gatemon qubits and topological superconductivity.

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Cuizuz Chang

Dr. Cui-Zu Chang

Date: 10/30/2020

Time: 1:00 PM - 2:00 PM

Location: Zoom (link to meeting)

 

Short Biography:

Dr. Chang is an assistant professor in the Department of Physics at The Pennsylvania State University. Chang received his Ph.D. in Physics in 2013 from Tsinghua University. Before joining Penn State, he did 4-year postdoctoral work at MIT. Chang is a world-leading expert in the molecular beam epitaxy (MBE) growth of quantum materials, particularly the quantum anomalous Hall (QAH) insulators. Chang was the first to realize the QAH effect using a magnetically doped topological insulator (specifically, Cr-doped (Bi,Sb)2Te3) thin film in 2013. His recent interests include the pursuit of high temperature and high Chern number QAH insulators and the exploration of Majorana physics in the QAH-superconductor hybrid structures. His awards include NSF CAREER Award (2019), ARO-Young Investigator Program Award (2018), Alfred P. Sloan Research Fellowship (2018), IUPAP Young Scientist Prize (2016), Macronix Prize (2019), and Gordon and Betty Moore EPiQS Materials Synthesis Investigator Award (2019).

Quantum Anomalous Hall Effect in the Magnetic
Topological Insulator Thin Films

The quantum anomalous Hall (QAH) effect can be considered as the quantum Hall (QH) effect without an external magnetic field, which can be realized by time-reversal symmetry breaking in a topologically non-trivial system [1, 2]. A QAH system carries spin-polarized dissipationless chiral edge transport channels without the need for external energy input, hence may have a huge impact on future electronic and spintronic device applications for ultralow-power consumption. The many decades quest for the experimental realization of QAH phenomenon became a possibility in 2006 with the discovery of topological insulators (TIs). In 2013, the QAH effect was observed in thin films of Cr-doped TI for the first time [3]. Two years later in a near-ideal system, V-doped TI, contrary to the negative prediction from first principle calculations [2], a high-precision QAH quantization with more robust magnetization and a perfectly dissipationless chiral current flow was demonstrated [4]. In this talk, I will also talk about our recent progress on QAH sandwich heterostructures from the axion insulator physics [5] to the concurrence of the QAH and topological Hall effects [6] and the QAH-superconductor devices about the absence of evidence for chiral Majorana fermion excitations [7].

 

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dr. Nahum Arav

Dr. Nahum Arav


DATE/TIME: 10/30/2020 3PM


Location: Zoom (Link to meeting)


Short Biography:


Nahum Arav got his PhD working with Mitch Begelman at the university of Colorado Boulder. He did a post-doc at Caltech with Roger Blandford and for the last 13 years he has been a physics professor at Virginia Tech.

The Contribution of Quasar Absorption Outflows to AGN Feedback

Determining the distance of quasar absorption outflows from the central source and
their kinetic luminosity is crucial for understanding their contribution to AGN feedback.

Here we summarize the results for a sample of nine luminous quasars that were observed with the Hubble Space Telescope. We find that the outflows in more than half of the objects are powerful enough to be the main agents for AGN feedback. The sample is

representative of the quasar absorption outflow population as a whole and is unbiased towards

specific distance ranges or kinetic luminosity value. Therefore, the analysis results can be extended to the majority of such objects, including broad absorption line quasars (BALQSO).

 

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Dr. Luis Jauregui

Dr. Luis A. Jauregui (“Howregee”)


DATE/TIME: 11/06/2020 2pm


Location:Zoom (Link to Meeting


Short Biography:


Luis A. Jauregui is an Assistant Professor at the University of California, Irvine and the Director of the Irvine Quantum Materials Center since 2019. His area of research is in the quantum transport and light matter interaction of quantum materials and devices. Dr. Jauregui was a Postdoctoral fellow at Harvard University until 2019 working in the light matter interaction of two-dimensional (2D) materials and devices. Dr. Jauregui obtained his PhD from Purdue University in 2016, working in the quantum transport of topological nanostructures, graphene and other 2D materials. Dr. Jauregui was the recipient of the Intel PhD fellowship in 2012 and the Purdue Research Foundation Fellowship in 2013.

Exciton manipulation in atomically thin heterostructures


Van der Waals heterostructures constructed of 2-dimensional (2-D) materials such as single layer transition metal dichalcogenides (TMDs) have sparked wide interest because of their large excitonic binding energy, allowing the exploration of novel quantum optical effects in a solid-state system and new opto-electronic devices. In this talk, I will discuss our results in van der Waals heterostructures formed by stacking together two different TMDs (forming a staggered heterojunction) encapsulated with hexagonal boron nitride (h-BN) with electrical contacts in each layer and a dual gate configuration. Interlayer excitons, with electrons and holes residing in spatially separated quantum wells, have long lifetimes (> 200 nanoseconds, 5 orders of magnitude longer than intralayer exciton lifetimes). Because of their repulsive Coulomb interaction, they “diffuse” across the entire sample (20 m long) driven by interaction, allowing their manipulation towards condensation. We used local electric fields to localize interlayer excitons, and increase their local exciton densities to few 1012 cm-2 allowing the observation of signatures of Mott transitions. Also, we observed and manipulated long-lived charged interlayer excitons, by electrostatically doping the sample. When the chemical potential reaches the second conduction band in a TMD (MoSe2) we demonstrated the electrical tunability from spin-singlet to spin-triplet charged interlayer excitons. Our long-lived charged interlayer excitons can be used as carriers for quantum information. Our results pave the way for novel optoelectronic devices as well as a step towards a solid-state platform for generating and exploring Bose-Einstein condensates at high temperatures, near-infrared tunable lasers and light emitting diodes.

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hannah jang-condell

Hannah Jang-Condell


DATE/TIME: 11/13/2020 4PM


Location: Zoom (Meeting Link


Short Biography:


Hannah Jang-Condell is an Associate Professor at the University of Wyoming in the Department of Physics & Astronomy. Her research interests include planet formation, theory and modeling of protoplanetary and debris disks, and exoplanet discovery and characterization.

Sabbatical, Interrupted


In the fall of 2019, Dr. Jang-Condell went on sabbatical, full of confidence that the experience would be rich and rewarding, and that it would invigorate her research program. COVID-19 had other ideas. In this talk, Dr. Jang-Condell will report on her sabbatical activities: what was planned, what was achieved, and what went up in smoke.

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dr. david clements

Dr David L Clements


DATE/TIME: 11/20/2020 3PM


Location: Zoom (Meeting Link)


Short Biography:


Dr Clements is a Reader in Astrophysics at Imperial College London. His PhD was also from Imperial. He has worked as a postdoc in Oxford, as an ESO Fellow, at the Institut d’Astrophysique Spatial in Orsay, and at Cardiff University. He returned to Imperial College in 2001 to work on the Herschel and Planck missions and became faculty there in 2009. His main research interests are in far-IR and submm extragalactic astronomy and cosmology, with a special interest in dusty star-forming galaxies. However, his broader interest have led him in recent years to apply submm techniques to the search for biosignatures in our own Solar System and collaboration with Prof Jane Greaves. The most recent outcome from this work is the surprising discovery of phosphine (PH3) in the cloud decks of Venus. The origin of this gas is unclear, but the fact that it is a potential biomarker has produced a lot of interest.

Phosphine Gas in the Cloud Decks of Venus

Ground-based observations of Solar System objects can test potential approaches for future biomarker searches on exoplanets. We thus observed the planet Venus with the JCMT in search of the potential biomarker phosphine, PH3. We expected to set only an upper limit for this absorption line, but instead detected a line indicating the presence of PH3 in the cloud decks of Venus at an altitude of about 55 km with an abundance of about 20 ppb. Further observations with ALMA confirmed the presence of this line, producing a detection at up to 15 σ significance, and provided some information on the distribution of the gas with latitude. The presence of phosphine remains unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently-known abiotic production routes in Venus' atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. Phosphine could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of phosphine on Earth, from the presence of life.

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andrew baczewski

Andrew D. Baczewski


DATE/TIME: 11/20/2020, 2-3PM MT


Location: Zoom (Meeting Link)


Short Biography:


Andrew Baczewski is a Principal Member of Technical Staff in the Quantum Computer Science group at Sandia National Laboratories. His research is focused on all aspects of quantum simulation on both classical and quantum computers, particularly as it applies to problems in materials science and condensed matter physics. Andrew has degrees in Physics and Electrical Engineering from Michigan State University, where he was a National Science Foundation Graduate Research Fellow. He joined Sandia National Laboratories as a postdoc in 2013 and became a staff scientist in 2014. He has also been an Adjunct Assistant Professor at the Center for Quantum Information and Control at the University of New Mexico since 2019.

How can classical and quantum computers team up to understand matters of substance?

Whereas classical computers require a choice between the two, among the promises of quantum computing is the ability to simulate physical systems both accurately and efficiently. Thus the realization and application of quantum information processing systems might lead to significant impacts in a wide range of disciplines, including chemical and materials sciences and nuclear and high-energy physics. But building such systems, which are large enough and robust enough to solve classically intractable problems, remains a long-term challenge. Tackling this challenge will require the use of classical computing tools to better understand, design, and manipulate the components of quantum computers and related technologies. I will give an overview of work that our group is doing in this area, touching on a range of topics that includes: (1) design of solid-state analog simulation platforms for studying Fermi-Hubbard physics, (2) understanding new physics in qubit-like semiconductor devices, (3) development of new approaches to simulation algorithms that are viable on today’s early and imperfect digital quantum computers, and (4) why you should be interested in quantum simulation as a promising technology for enabling physics research in years to come.
Sandia National Laboratories is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. The views expressed in this abstract do not necessarily represent the views of the DOE or the U.S. Government.

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