Speaker Series FA2020

Sep. 10th, PROF. Rachel Goldman

Material Science

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.

Sep. 24th, PROF. Christine Aidala

Experimental High-Energy Nuclear Physics

Title: Pulling Apart the Strong Force by Peering Into the Proton

Abstract: Protons are at the core of every atom, forming the atomic nucleus along with their uncharged partners, neutrons. As tiny as they are, we know that protons are comprised of yet tinier subcomponents, quarks and gluons, which are continuously interacting with one another through the strong force. Even though the strong force is one of only four known forces in nature along with gravity, electromagnetism, and the weak force, we still have a lot to learn about how quarks and gluons lead to the rich and complex internal workings of this basic building block of everyday matter.

Recorded talk:

Oct. 8th, Prof. Qiong yang

Biophysics of Living Systems

Title: Building a synthetic cell: Understanding the clock design and function

Recorded Talk:

Oct. 22nd, Prof. Lydia Bieri

Mathematical Physics and General Relativity

Title: Gravitational Waves and Their Sources

Abstract: Gravitational waves from distant sources travel through the Universe. They are produced when black holes or neutron stars merge or in a core-collapse supernova. We may think of these waves as ripples in spacetime, changing the curvature of the latter. Spacetimes are solutions of the Einstein equations in General Relativity (GR). These equations describe the laws of the Universe, giving them a geometric structure. In 2015, gravitational waves were observed for the first time by Advanced LIGO (and several times since then), marking the beginning of a new era. Gravitational radiation carries a wealth of information about their sources. Studying solutions of the Einstein equations, we derive knowledge about these sources that help us identify the message encoded in gravitational waves. The Universe even `remembers' the passage of a wave train. The latter has interesting structures and is expected to be observed in the near future. We will explore gravitational waves, typical sources and tools to investigate them.

Recorded talk:

Nov. 5th, ProF. Bjoern Penning

Experimental Dark Matter Detection

Title: Searching for Dark Matter from the Lowest to the Highest Energies

Abstract: Dark Matter (DM) is a long standing puzzle in fundamental physics and the goal of a diverse research program. In underground experiments we search for DM directly using lowest possible energy thresholds, at collider we seek to produce dark matter at the very highest energies, and using telescopes we look for telltale signatures in the cosmos. All these detection methods probe different parts of the possible parameter space. I will highlight the status of existing and upcoming experiments including new direct detection experiments with world leading sensitivities to start data taking in late 2020/20201.

Recorded talk:

Nov. 19th, ProF. Gordon Belot

Philosophy of Physics

Title: Can We Know the Shape of Space?

Dec. 3rd, ProF. Tom Schwarz

Experimental High-Energy Particle Physics

Title: Research with the ATLAS Experiment at the Large Hadron Collider

Abstract: I will discuss our team's recent work in studying the properties of the Higgs Boson and searching for new physics associated with the production of Higgs - in particular, searching for Higgs Boson decay to second generation particles and the production of two Higgs Bosons in a single event. I will also present current efforts at Michigan to upgrade the ATLAS detector, including the production of new detectors and high-speed electronics for readout.

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