Zu, Tianrui - University of California, Berkeley

Non-Equilibrium Dynamics of a BCS Superconductor

Recently developed experimental tools that control and probe many-body quantum systems have provided access to new time and length scales of various quantum systems. Techniques such as pump-probe experiments and cavity quantum electrodynamics have enabled us to explore and understand the phases and orders of previously difficult-to-study many-body systems such as the Cuprate superconductors.

Here, I will present our theoretical investigations of a non-equilibrium BCS system with a time-varying order parameter. We focus on the transient dynamics of such systems, and developed a theory using the Baym-Kadanoff-Keldysh formalism that enables us to study the dynamics of the system in contact with a thermal bath for dissipation. We then use our theory to look at two different types of gap dynamics. First, we try to understand some measurements of a type of pump-probe experiment: the time- and angle-resolved photoemission spectroscopy (tr-ARPES), and discuss the limit of the quasi-static method currently used to understand these measurements. Second, we study the gap dynamics of a BCS system initially prepared in some time-reversal-breaking states, and found a possible Higgs mode in such systems.