Ph.D. Candidate: Ilya Esterlis
Research Advisor: Steven A. Kivelson
Date: Monday, June 3, 2019
Time: 10:00 AM
Location: Hewlett Building, Room 102
Title: Reconsidering the electron-phonon problem
Abstract: One of the most important interactions in a solid is that between electrons and the vibrational modes of the underlying lattice (phonons). This interaction determines many of the familiar features of conventional metals, e.g. resistivity at elevated temperatures, as well as their superconducting transition temperature, Tc. From a theoretical standpoint, the electron-phonon problem was considered to be solved 60 years ago, thanks to the pioneering work of Migdal and Eliashberg. We have revisited this problem using a combination of numerical and analytic techniques, and I will show that this "solved” problem harbors basic features that have not been properly understood. I will show that the Migdal-Eliashberg approach works remarkably well for sufficiently weak coupling but breaks down entirely as the coupling strength is increased (even while the nominal condition for its validity remains intact), giving way to a qualitatively new regime of strong coupling physics. I will discuss the implications of these results for superconductivity and argue they suggest an approximate, universal upper bound on Tc in conventional metals.