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Events on Thursday, April 18th, 2024

R. G. Herb Condensed Matter Seminar
New twists on topology in moiré quantum matter
Time: 10:00 am - 11:00 pm
Place: 5310 Chamberlin
Speaker: Matthew Yankowitz, U Washington
Abstract: Moiré patterns formed by stacking atomically thin van der Waals crystals can give rise to dramatic new physical properties, in select cases generating flat bands that host a variety of intertwined correlated and topological states of matter. I will discuss two distinct moiré platforms that each exhibit their own unique topological properties. The first is twisted bilayer-trilayer graphene, in which we observe the formation of generalized anomalous Hall crystals that either triple or quadruple the area of the moiré unit cell. These states exhibit a fully-developed integer quantum anomalous Hall effect, with a Chern number that can be flipped between +1 and -1 by out-of-plane or in-plane magnetic fields or by an electric displacement field. The second system we study is twisted molybdenum ditelluride (tMoTe 2 ), which was recently found to host the fractional quantum anomalous Hall effect. By probing tMoTe2 on the atomic scale using scanning tunneling microscopy and spectroscopy, we are able to detect fingerprints of the layer pseudospin skyrmion lattice responsible for generating the topology of the moiré bands. Our findings showcase the diverse range of novel topological properties that can arise in moiré materials.
Host: Alex Levchenko
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Hunting for Galactic PeVatrons in the X-ray Regime
Time: 2:30 pm - 3:30 pm
Place: CH 5310
Speaker: Shuo Zhang, MSU
Abstract: Cosmic rays with energies up to a few PeV are believed to originate from our own galaxy. However, the origin of Galactic cosmic-rays has remained a mystery for over a century since their discovery. The H.E.S.S. observatory discovered a PeVatron within 10 parsecs of the center of our galaxy, which suggests that the supermassive black hole Sgr A* may be responsible. Despite being one of the least active supermassive black holes, Sgr A* may have acted as a potent particle accelerator during its active stage in the past. In this talk, I will describe our attempts to find multi-wavelength observational evidence that Sgr A* used to be a PeVatrons, as well as how we can reconstruct Sgr A* activity history in the past few million years. I will also introduce our ongoing observational efforts to identify other Galactic PeVatron candidates discovered by LHAASO and to test whether they bear a nature of supernova remnants, pulsar wind nebula or else.
Host: Lu Lu
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Wisconsin Quantum Institute Seminar
Visible-Light Photonic Integration for Atomic and Quantum Sciences and Applications
Time: 3:30 pm - 5:00 pm
Place: Discovery Building, DeLuca Forum
Speaker: Daniel J Blumenthal, University of California Santa Barbara

Visible-light integrated photonics will enable compact, reliable quantum and atomic experiments. Integration also has the potential to bring about improved performance and scalability as well as new functionality for sensing, computation, clocks, and metrology. We discuss progress in ultra-low-loss silicon nitride integration for precision lasers, modulators, and other atomic and quantum related photonics. We will also describe progress towards higher-level functionality integration in experiments and applications that involve cold atoms, trapped ions and neutral atoms.

This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Xuting Yang (Jennifer Choy group), titled "Atomic magnetometry using a metasurface polarizing beamsplitter". The invited presentation starts at 4pm.

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Astronomy Colloquium
NIRWALS: the Near InfraRed Washburn Astronomical Laboratories Spectrograph on SALT
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Marsha Wolf, UW-Madison
Abstract: Advances in astronomical instrumentation propel our understanding of the universe. One example is how integral field spectroscopic surveys of thousands of nearby galaxies over the last decade have revealed unprecedented spatially-resolved views into the details of galaxy evolution. The University of Wisconsin Astronomy Department’s Washburn Astronomical Laboratories specializes in integral field instrumentation. We were involved in the SDSS-IV MaNGA survey that observed 10,000 galaxies, recently commissioned the Near InfraRed Washburn Astronomical Laboratories Spectrograph (NIRWALS) on the 11-meter Southern African Large Telescope (shared-risk science observations begin in May 2024), and are currently developing a speckle imaging integral field spectrograph for the Lowell Discovery Telescope. This talk will focus on NIRWALS with descriptions of its development history, capabilities, early performance on SALT, and a preview into new galaxy evolution studies that it will enable. The near infrared spectral band allows access to nebular lines that are tracers of dust-obscured star formation, AGN activity, and shocks, providing a critical probe into galaxy quenching processes. Recent ALMA observations have shown that post-starburst galaxies, in which optical spectra indicate that star formation has been rapidly quenched, still contain significant reservoirs of gas. So, what stopped the star formation? We are launching a new project to observe 50 post-starburst galaxies with NIRWALS, using them as laboratories to investigate whether their star formation is still ongoing, but hidden by dust, or whether feedback from AGN or galactic winds have depressed star formation efficiency by dominating the ISM energetics in these galaxies.
Host: Ke Zhang
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