PHYSICS PH.D. DISSERTATION DEFENSE: Benjamin Nosarzewski

Ph.D. Candidate: Benjamin Nosarzewski

Research Advisor: Thomas Devereaux

Date: Tuesday, Sep 29, 2020

Time: 1:00 PM

Zoom Meeting Link: https://stanford.zoom.us/j/94977742441

Zoom Meeting Password: Email mariaf67 [at] stanford.edu (mariaf67[at]stanford[dot]edu) for password

Title: Numerical Studies of Electron-Phonon Mediated Superconductors

Abstract: 

In conventional metals, the interaction between electrons and the vibrational modes of the underlying lattice is responsible for many properties ranging from resistivity at high temperatures to the formation of superconducting and charge-density wave order at low temperatures. Using numerical methods for many-body perturbation theory as well as exact Quantum Monte Carlo methods, we study the properties of electron-phonon systems both in and out of equilibrium and make connections to various quantities measurable through experimental methods such as angle-resolved photoemission spectroscopy (ARPES) and time-resolved ARPES (tr-ARPES). We analyze the real-frequency solutions of a self-consistent many-body perturbation theory which accounts for both the electron and phonon self-energies and discuss the effects of phonon softening, electron mass enhancement, differences in two common definitions of the electron-phonon coupling constant, and the ratio of the superconducting gap size to the superconducting transition temperature in conventional superconductors beyond the weak-coupling limit described by Bardeen-Cooper-Schrieffer theory. We also simulate the pump-probe process of tr-ARPES to illustrate a novel way of measuring the momentum-resolved electron-phonon coupling constant from the rates of quantized electron relaxation processes due to scattering from an optical phonon mode. Finally, we characterize the frequency and momentum dependence of the Higgs mode in a superconductor with d-wave pairing symmetry and describe the signatures expected to be visible in tr-ARPES experiments.