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
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Title: Numerical Studies of Electron-Phonon Mediated Superconductors
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.