SEMINAR 2025
Switch between continuous and discontinuous transition at 2d Nematic transition/Stoner Instabilities via Field-Theoretical RG
| Speaker | Han Ma, Stony Brook University, USA |
| Date/Time | Friday, 15 Aug, 11am |
| Location | S11-02-07 Conference Room |
| Host | Asst/Prof Zou Liujun |
Abstract
I will talk about my work on the fixed-point structure of an interacting two-flavor fermionic system, applicable to Moiré systems near the valley polarization transition, where each flavor possesses a dispersion with a tunable real exponent “a”. Starting from the Fermi liquid phase at weak interaction, we identify two possible Pomeranchuk/Stoner-type instabilities at stronger interaction. These instabilities lead to spontaneous spatial rotational or flavor symmetry breaking. Our key discovery is that one of these instabilities exhibits an RG fixed point that is attractive for “a<1”, indicating a continuous transition. Conversely, for “a>1”, the fixed point becomes repulsive, resulting in a discontinuous transition. We also investigate the collective modes driving these instabilities of Fermi liquids. This work predicts a universal ratio between collective modes and Fermi surface sizes at the continuous transition instability, which is experimentally observable.
Biography
Han Ma is an assistant professor in the physics department at Stony Brook University. Before joining Stony Brook in the spring of 2025, Han Ma was a postdoc at the Perimeter Institute for Theoretical Physics. She received a Ph.D. in Physics from University of Colorado Boulder, USA and a B.S from Fudan University, Shanghai, China.
Han Ma’s research focuses on exotic quantum phases characterized by long-range entanglement, emergent gauge structures, and universal scaling behaviors. Her works span the full spectrum of quantum phases of matter, from topological phases like fractons and Kitaev spin liquids, to critical systems described by complex conformal field theory, and correlated metallic phases with Fermi surface.