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2:30 pm - Topological Defect Networks - A Framework for Fractons
Speaker: Danny Bulmash
Abstract: Fracton phases exhibit striking behavior, including deconfined excitations which cannot move freely in isolation and subextensive ground state degeneracy, which appears to render them beyond the standard topological quantum field theory (TQFT) paradigm for classifying gapped quantum matter. Here, we show that topological defect networks---networks of topological defects embedded in “stratified” 3+1D TQFTs---provide a unified framework for describing various types of gapped fracton phases. In this picture, the sub-dimensional excitations characteristic of fractonic matter are a consequence of mobility restrictions imposed by the defect network. We conjecture that all gapped phases, including fracton phases, admit a topological defect network description and support this claim by explicitly providing such a construction for many well-known fracton models. Reference: arXiv: 2002.05166
3:00 pm - Dynamics of Renyi entropy in coupled Brownian SYK model
Speaker: Shaokai Jian
Abstract: We study the time evolution of Renyi entropy between two coupled Brownian SYK models starting from a product state. The Renyi entropy grows linearly and then saturates to the coarse grained entropy. This Page curve is obtained by two different methods, the saddle point analysis and the operator dynamics. As a Brownian circuit, the Page curve is governed by operator dynamics, which we derive in the form of the master equation. Behind this complicated master equation, a more physical explanation is revealed with the help of saddle point method: the replica-diagonal and replica-wormhole saddles are responsible for the linear growth and the saturation of Renyi entropy, respectively.
3:30 pm - Fermi surface topology and quasiparticle properties in an anisotropic electron gas
Speaker: Seongjin Ahn
Abstract: We have carried out a comprehensive investigation on the renormalized Fermi surface and the quasiparticle properties in a two-dimensional electron gas in the presence of mass anisotropy. We first show that the interacting Fermi surface deviates from an ellipse, but not in an arbitrary way: The interacting Fermi surface has only two qualitatively distinct shapes, and its deviation from an ellipse is quantitatively rather small except for very low electron density, providing justification for the widely used elliptical Fermi surface approximation. We then investigate the quasiparticle properties by calculating the self-energy, the spectral function, the scattering rate, and the effective mass. We find novel anisotropic features of quasiparticle properties that are not captured by the commonly used isotropic approximation where the anisotropic effective mass is replaced by the isotropic averaged density-of-state mass. Reference: arXiv: 2002.12532