PhD Defenses


Fri May 20th 2022, 4:00 - 5:00pm
McCullough 335
Stanford overview

Photo by Linda Cicero

Ph.D. Candidate:  Jacob Marks

Research Advisor: 
Tom Devereaux

Co-advisor: Xiaoliang Qi

Date: 05/20/2022
Time: 4 PM PDT

Location: McCullough 335

Zoom Link:

Zoom Password: email for password.


Title: The Surprising Persistence of Symmetry Protected Topology

Abstract: In 1980, while subjecting semiconductors at low temperatures to strong magnetic fields, Klaus von Klitzing observed a surprising exact quantization in transverse resistivity. This phenomenon, which has been confirmed to three parts per ten billion, was subsequently explained by the integer quantum Hall effect, forever altering our understanding of what is possible in correlated electron materials.


In the first part of my talk, I will introduce topology, the branch of mathematics that underpins this phenomenon. I’ll speak about topological materials and their applications, and I’ll compare topological order with the Landau symmetry breaking paradigm. I’ll end this section by introducing symmetry protected topology, which is responsible for all topological insulators and superconductors, and highlighting the rigidity of established frameworks for categorizing this physics.


The remainder of my talk will argue for the inadequacy of these frameworks in explaining the robustness of symmetry protected topological phenomena. Focusing on the paradigmatic model for a topological insulator, the Su-Schrieffer-Heeger model, I will discuss two scenarios in which signatures of topology persist beyond the established frameworks. First, I will show that quantized charge transport is still possible when protecting symmetries are broken. Second, I will demonstrate that even out of equilibrium, signatures of topology can be identified on both single particle and many body levels. I will conclude with a brief outlook.