Passcode: 862998

In this talk, I will explore the interplay of interactions and disorder in topological quantum systems, focusing on both their influence on the system’s properties and the eventual breakdown of topological phases. I will first discuss how these factors modify the system’s behavior before its collapse, highlighting the emergence of prominent surface collective modes, which serve as experimental signatures of non-trivial topology, and spatially dependent order parameters. While topological systems are inherently resilient to disorder and interactions, I will examine the conditions under which these phases break down, delineating the boundaries of their stability. In particular, I will analyze how disorder and strong interactions influence the density of states, leading to the destruction of topological surface modes, often through a cascade process where higher-order topological phases vanish first. Both mean-field and beyond mean-field approaches will be discussed, highlighting universal and non-universal features. These insights offer a comprehensive view of the resilience and ultimate breakdown of topological phases under external perturbations.

Stephan Haas was born in Berlin and spent his early years in both Germany and Japan, gaining exposure to diverse cultural and educational environments. He began his academic journey in physics at the Technische Universität Berlin, where he earned his Vordiplom in Physics in 1990. To further his studies, Stephan moved to the United States and completed his Ph.D. in Physics at the National High Magnetic Field Laboratory at Florida State University in 1995, focusing on theoretical quantum systems.

Following his doctorate, Stephan undertook a postdoctoral fellowship at the Swiss Federal Institute of Technology, where he expanded his research into quantum condensed matter physics. In 1998, he joined the faculty at the University of Southern California, where he has been a member of the Department of Physics and Astronomy.

At USC, Stephan Haas and his research group focus on topics including quantum magnetism, superconductivity, and quantum information theory. Their work investigates microscopic models of interacting quantum systems, employing numerical techniques like Quantum Monte Carlo, Renormalization Group, and Exact Diagonalization to explore phase diagrams, ground states, and dynamical properties. Recently, his research has focused on the effects of interactions and disorder in topological quantum systems.