Correlation-enhanced electron-phonon interaction in oxide superconductors from GW perturbation theory*

Accurate and practical ab initio treatment of electron-phonon (e-ph) coupling is essential to the understanding of many condensed-matter phenomena. In this talk, I will present a recently developed ab initio linear-response method named GW perturbation theory (GWPT) that computes the e-ph interaction with the inclusion of the GW nonlocal, energy-dependent self-energy effects. GWPT goes beyond the commonly used density-functional perturbation theory (DFPT), which becomes inadequate in some materials when correlation effects are non-negligible. We demonstrate the GWPT method by showing that the e-ph coupling in Ba_1-xK_xBiO₃ is significantly enhanced by many-electron correlation, strong enough to explain its high superconducting Tc of 32 K. Furthermore, GW-level anisotropic Eliashberg equation calculations suggest that infinite-layer nickelate superconductor Nd_1-xSr_xNiO₂ may host a strong phonon-mediated s-wave two-gap superconductivity. I will also present studies on the e-ph coupling in cuprates and discuss new understanding in phenomena such as the ubiquitous 70-meV nodal dispersion kink.