Physics Colloquium - Current

Speaker:  Dr. Scott Jensen, University of Illinois

Abstract:

Since their development in the 1950s and 60s, Quantum Monte Carlo (QMC) methods have become essential computational tools for exploring strongly correlated systems across nuclear, chemical, and condensed matter physics. Despite substantial progress, major challenges remain in understanding certain paradigmatic systems, motivating ongoing advances in QMC. For instance, predicting high-pressure structures and phase transitions in the hydrogen phase diagram is particularly challenging. In the arguably simpler system of the unitary Fermi gas (UFG), a paradigm model for strongly correlated superfluids, qualitative properties in the so-called “pseudogap regime” remain debated. This regime is characterized by pairing correlations that persist above the superfluid transition temperature.

In this talk, I will discuss recent advances in QMC methods that enable controlled calculations for the UFG. I will then introduce machine-learned interatomic potentials that achieve QMC-level accuracy for dense hydrogen, presenting new findings that support our recent prediction of a high melting line up to 180 GPa. Finally, I will share recent results on the liquid-liquid phase transition (LLPT) in hydrogen and its implications for future theoretical studies.

Speaker: Dr. Karen Masters, Haverford College Dept. of Physics & Astronomy

Abstract: The iconic spiral arms that decorate the disks of massive galaxies (like our own Milky Way) have been studied observationally and theoretically since they were first recorded 180 years ago, nevertheless the exact details of their nature remains elusive. I will review what is known observationally about spiral arms, including results from the citizen science project Galaxy Zoo (www.galaxyzoo.org) and the large galaxy survey “MaNGA” (Mapping Nearby Galaxies at Apache Point Observatory - part of the SDSS). I will discuss how these and other observational data are being used to constrain the variety of different physical models which have been proposed to explain spiral arms in galaxies.

This talk is supported by the Brown and Williamson Foundation.

Speaker:  Dr. Chunli Huang, University of Kentucky

Abstract:  Recent investigations have established lightly-doped rhombohedral multilayer graphene as an exceptional material for probing electronic phases that arise from strong Coulomb interactions and non-trivial band topologies. This talk will discuss advancements in experimental techniques that have deepened our understanding of electronic behaviors in these systems. We adopt a generalized electron gas model to study the interaction effects in these systems. We present a self-consistent mean-field phase diagram and use time-dependent mean field theory to study their spin-valley paramagnon/ferromagnon excitations. A special focus will be given to unconventional orbital magnetism in the so-called quarter-metal phase. This talk is based on the review article available at arXiv:2408.15884.