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Events on Monday, March 18th, 2024

R. G. Herb Condensed Matter Seminar
Quantum skyrmion Hall effect
Time: 12:00 pm - 1:00 pm
Place: 5310 Chamberlin Hall
Speaker: Ashely Cook, Max Planck Institutes for the Physics of Complex Systems and the Chemical Physics of Solids
Abstract: In the quantum Hall effect, a two-dimensional gas of electrons is subjected to an out-of-plane magnetic field and electron transport quantises: the Hall conductivity plateaus at values proportional to integers and rational numbers in units of fundamental constants, with remarkably low error. Shortly after experimental discovery of the quantum Hall effect in 1980, theorists developed a framework explaining this quantization as a consequence of topological phases of matter, or those phases with signatures unaffected by sufficiently small perturbations. In particular, a theory in terms of point charges coupling to external fields beautifully described this physics. A great variety of topological phases have been classified as a consequence of discovery of the quantum Hall effect, but this work has recently led to discovery of topological skyrmion phases of matter, multiplicative topological phases of matter, and finite-size topological phases of matter, which contradict key assumptions of established classification schemes. The discovery of these three sets of topological states necessitates a paradigm shift from the quantum Hall effect framework to that of the quantum skyrmion Hall effect, in which the point charges of the quantum Hall effect are generalised to truly quantum counterparts of topological textures in observable fields, called skyrmions.
Host: Alex Levchenko
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Plasma Physics (Physics/ECE/NE 922) Seminar
"Cylindrical Implosion Experiments at Los Alamos National Laboratory"
Time: 12:00 pm - 1:15 pm
Place: 1227 Engineering Hall
Speaker: Josh Sauppe, LANL (Los Alamos National Laboratory)
Abstract: The advent of high-power laser facilities such as the National Ignition Facility (NIF) has ushered in a new and exciting era in high-energy-density (HED) physics research, and the flexibility of the NIF allows many distinct targets to be fielded beyond the standard indirect-drive inertial confinement fusion (ICF) configuration. Los Alamos scientists are using directly driven cylindrical implosion experiments at the NIF to study hydrodynamic instability growth in regimes relevant to ICF systems, as cylinders enable direct measurements by viewing down the cylinder axis. These physical systems are often modeled in more tractable two-dimensional (2D) simulations with assumed symmetry, but this simplification risks inadvertently masking crucial features. Here, we show experimental evidence of a 3D asymmetry in directly driven cylindrical implosions which was not predicted with 2D modeling, and we accurately reproduce this feature in 3D simulations. The asymmetry arises from the NIF beam geometry and the dependence of laser absorption on beam incidence angle, and we also find that there is a north/south skew to the drive asymmetry. This skew is obscured in radiographs that image down the cylinder axis, complicating inferences of instability growth. This has significant implications for targets with off-normal beam pointing such as polar direct-drive ICF, and it may also be important for a more complete understanding of indirect-drive systems. In particular, differences between experimental data and synthetic data generated from 2D simulations can be misattributed to deficiencies in physics models rather than 3D effects. A similar but more subtle 3D effect is also identified for smaller-scale cylindrical implosion experiments fielded at the OMEGA laser facility, and this is confirmed in recent experiments.
Host: Prof. Carl Sovinec
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