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Events on Thursday, February 13th, 2025

R. G. Herb Condensed Matter Seminar
Past, present, and future of Superconducting Diode Effects
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Daniel Shaffer , UW-Madison
Abstract: The critical current in superconducting systems that lack both time reversal and inversion symmetries is generally non-reciprocal, i.e. unequal in magnitude for opposite current flow directions. This effect — called the superconducting diode effect (SDE) in bulk superconductors and the Josephson diode effect (JDE) in Josephson junctions — has attracted a lot of attention among both experimentalists and theorists, promising many applications for superconducting electronics. Nevertheless, a proper theoretical description of SDE has been challenging both on the phenomenological and microscopic levels, even for the simplest canonical model of the helical non-centrosymmetric superconductor with Rashba spin-orbit coupling (SOC) and in-plane magnetic field. Despite the relative simplicity of the model, several conflicting results have been obtained in the literature, including a prediction of the absence of SDE in the weak field limit. In this talk, I will review some of these controversies and present our resolution, which underscores the subtlety of the effect. Building on this understanding, I will also discuss several new microscopic mechanisms that we proposed for realizing or enhancing the SDE in disordered Rashba superconductors, as well as generic multiphase superconductors like UPt3 and UTe2.
Host: Alex Levchenko
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Atomic Physics Seminar
Making and probing Bose-Einstein condensates of polar molecules
Time: 11:00 am - 12:00 pm
Place: 5310 Chamberlin
Speaker: Dr. Ian Stevenson, Columbia University
Abstract: Recently, our lab realized the first BEC of polar molecules. By eliminating two- and three-body collisional losses via double microwave shielding, gases of sodium-cesium molecules are evaporatively cooled to quantum degeneracy. The BEC reveals itself via a bimodal momentum distribution when the phase-space density exceeds one. In this talk, I will share our latest insights into controlling the dipolar interactions in the BEC. Notably, we find that as dipolar interactions increase, their characteristic length scale exceeds the interparticle separation, signifying the onset of strong interactions.
Host: Mark Saffman
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Astronomy Colloquium
Vera C. Rubin Observatory On-sky Commissioning
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Keith Bechtol, University of Wisconsin-Madison
Abstract: The Vera C. Rubin Observatory is poised to begin a wide, fast, and deep imaging survey of the entire night sky visible from Chile's Atacama desert with the goal of measuring more stars, galaxies, optical transients, and Solar System objects during its first year of science operations in 2025-2026 than all previous cosmic surveys combined. In October-December 2024, Rubin Observatory conducted a 7-week on-sky commissioning campaign using an engineering camera as a first full-system test of hardware, software, and operational procedures. The next months are focused on installation and first night sky images with the full LSST Camera. I will discuss the pathway from commissioning to realizing first cosmology results with Rubin Observatory, and highlight ways for our local UW-Madison astrophysics community to get involved with Rubin Observatory science.
Host: Melinda Soares-Furtado
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