Speaker Series WN2021

Feb. 11th, PROF. Hui deng

Experimental Condensed Matter Physics

Title: Controlling Light-Matter Couplings for New Science & Technology

Abstract: Control and understanding of light and matter coupling are ubiquitous and of fundamental importance in modern science and technology. Recently developments in materials, photonics and condensed matter physics have opened doors to exciting new opportunities to create light-matter coupled systems unavailable before, which on one hand may provide an experimental testground of novel nonlinear, many-body and/or quantum phenomena, and on the other hand may serve as a bridge between such phenomena and better technology for the future. I will discuss a few recent and future topics under this theme, using unconventional exciton-polariton systems and two-dimensional materials.

Feb. 25th, Prof. Keith Riles

Experimental Cosmology and Astrophysics

Title: Gravitational Wave Astronomy -- Listening to the Universe

Abstract: Gravitational waves are minute disturbances of space itself, which can arise from distant and massive but compact bodies, such as black holes and neutron stars. Using them, scientists are probing some of the most exotic phenomena in the Universe. Insights from discoveries made so far, including some surprising new objects, will be presented, along with the potential for new discoveries that will make gravitational waves essential to the next century of astronomy and cosmology.

mar. 25th, Student talks

Andrew Gardner

Title: A Relaxation Treatment for Cluster Samples

Abstract: In cosmology, the mass of a galaxy cluster is a vital parameter for performing subsequent cosmological constraints. However, these cosmological measurements require low scatter proxies of the total galaxy cluster mass. We can use observable signatures of the galaxy cluster gas, such as the X-ray inferred cluster mass. Gas-based mass proxies are low scatter if the cluster is dynamically relaxed. Gas observable derived masses of relaxed clusters can be estimated with higher accuracy making them powerful probes of cosmology. The criteria for cluster relaxedness is not a well established procedure with several criteria being employed by observers and simulators. Little is known on how well these relaxation parameters’ regimes relate to one another, as well as how they correlate at different regions within a galaxy cluster and with thermodynamic properties of the cluster. In collaboration with The Three Hundred Project, which produced the galaxy cluster simulation data, and observational cosmologists who constrain parameters from gas fraction measurements, this research focuses on exploring the relationship between relaxation parameters used by both observers and theorists, and identifying physical mechanisms driving correlations.

Laura Zichi

Title: Graphene Monolayer Detecting Through Machine Learning

Abstract: Graphene monolayers have a myriad of technological applications. In order to optimize the construction of the flakes, I utilize various machine learning algorithms on microscope images to automate the extremely time consuming process of identifying monolayers, bilayers, or trilayers.

Grant Weldon

Title: Tilt-to-length couplings in the LISA gravitational wave detector

Abstract: The Laser Interferometer Space Antenna (LISA) will be the first space-based gravitational wave detector. LISA is expected to observe millihertz-frequency gravitational waves from Galactic white dwarf binaries, merging supermassive black holes, and potentially many other sources. Tilt-to-length (TTL) couplings are an expected noise source in LISA data, which arise from angular jitter of instrument components coupling into the interferometric measurement axis. We conduct a preliminary investigation of TTL noise in simulated LISA data and characterize the magnitude of coupling by coupling coefficients. We assess our ability to mitigate TTL noise by fitting for these coupling coefficients and coherently subtracting the fitted noise from instrument data. We also investigate how this procedure will affect searches for gravitational wave signals in the relevant frequency band.

Marius Kongsore

Title: To Find Light in the Darkness: Searching for Decaying Dark Matter Particles through Astrophysical X-ray Observations

Abstract: There is an overwhelming amount of evidence pointing to the existence of dark matter. All of this evidence is entirely consistent with dark matter being a new elementary particle not described by the Standard Model. I give a brief overview of the state of particle dark matter theory and phenomenological searches, and present my own work on searching for decaying dark matter particles through XMM-Newton X-ray telescope observations. Based on: https://arxiv.org/abs/2102.02207

apr. 8th, ProF. Liliana borcea

Mathematical Physics

Title: On the continuum limit of inverse spectral problems

Abstract: I will discuss a classic inverse spectral problem for a Sturm Liouville differential operator in a bounded interval, which models an oscillating string. The inverse problem is to determine the composition of the string from measurements of the displacement at one end. I will explain how one can use tools from numerical linear algebra and reduced order modeling to solve this problem. I will also comment on how the simple ideas in this talk can be used for solving more challenging inverse problems.

Apr. 22Nd, Prof. Rachel Goldman

Condensed Matter Physics and Engineering

Title: Surface Dimer Engineering of Highly Mismatched Alloys

Abstract: Highly mismatched "designer" alloys are materials that contain chemical elements with very different atomic sizes and abilities to attract nearby electrons. When a few atoms with larger or smaller atomic sizes are added to a host material, its electrical and optical properties often change dramatically. For example, the incorporation of dilute fractions of nitrogen and bismuth solute atoms into III-V semiconductors induces significant energy bandgap narrowing; thus, emerging dilute-nitride-bismuthide alloys are of significant interest for long-wavelength applications ranging from temperature-insensitive laser diodes to ultra-high efficiency multijunction photovoltaic cells. While the properties of emerging dilute-nitride-bismuthide alloys are highly sensitive to local atomic environments, the solute incorporation mechanisms are not well understood. In this talk, we present combined computational-experimental studies which enabled our pioneering epitaxy and band structure engineering of GaAs(N):Bi alloys. In addition to describing recent advances in surface reconstruction-driven control of solute incorporation[i]^,^[ii] and atomic-ordering,[iii] we present a new “magic ratio” for lattice matching of GaAsNBi with GaAs substrates.[iv] We also present a strategy for the synthesis and tailored electronic structure of III-V bismuthides for integration with III-V based electronics.

This work was supported by the National Science Foundation (Grant Nos. DMR 1410282 and 1810280), the Center for Integrated Nanotechnologies, jointly operated by Los Alamos and Sandia National Laboratories for the U.S. Department of Energy (DoE), and the Office of Science Graduate Student Research Program, administered by the Oak Ridge Institute for Science and Education for the U.S. DoE.

Biography:

Rachel S. Goldman is Professor of Materials Science & Engineering, Physics, and Electrical Engineering & Computer Science at the University of Michigan. She is Associate Director of Applied Physics, and has served as MSE Graduate Chair, Associate Director of the DoE Energy Frontiers Research Center, and Education Director of the NSF Materials Research Science and Engineering Center. Prof. Goldman's research emphasizes the materials physics of semiconductors, with a recent focus on dilute nitride-bismuthide "magic" alloys. She has published > 130 papers on processing-structure-property correlations in semiconductors; she holds a U.S. patent on “ion-cut-synthesis”, a novel approach for simultaneous synthesis and integration of nanocomposite materials with virtually any substrate. Prof. Goldman is a Fellow of the American Physical Society (APS) and the American Vacuum Society. She is Associate Editor of the Journal of Applied Physics and Chair-Elect of the APS Division of Materials Physics.

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