Nicholas Metropolis Award for Outstanding Doctoral Thesis Work in Computational Physics (2021): Correlation-enhanced electron-phonon interactions in oxide superconductors from linear-response GW perturbation theory*

A general, accurate and practical ab initio treatment of electron-phonon (e-ph) coupling is essential to the understanding of many excited-state phenomena. In this talk, I will present a new ab initio linear-response method named GW perturbation theory (GWPT) [1] that computes the e-ph interaction with the inclusion of the GW nonlocal, energy-dependent self-energy effects, going beyond the commonly used density-functional perturbation theory, which is inadequate in some materials. We apply GWPT to study e-ph interaction in oxide superconductors. We first show that the e-ph coupling in Ba_1-xK_xBiO₃ is significantly enhanced by many-electron correlations, and is strong enough to explain its high superconducting T_c of 32 K as well as its doping dependence [1]. Secondly, with this method, we study a two-decade-old mystery – a ubiquitous 70-meV dispersion kink in cuprates observed in angle-resolved photoemission experiments, whereas the debate on its physical origin is yet to be settled. I will show, with ab initio GWPT results on the prototypical cuprate La_2-xSr_xCuO₄, that the computed correlation-enhanced e-ph interaction gives rise to strong nodal kinks in quantitative agreement with experiments [2]. This study also provides new insights to the observed doping dependence of the photoemission kink in the cuprates.

[1] Z. Li, G. Antonius, M. Wu, F. H. da Jornada, and S. G. Louie, Phys. Rev. Lett. 122, 186402 (2019).
[2] Z. Li, M. Wu, Y.-H. Chan, and S. G. Louie, “Unmasking the origin of photoemission kinks in the Cuprates,” submitted.