Time-Domain ab Initio Modeling of Electron-Phonon Relaxation in High-Temperature Cuprate Superconductors

Superconducting pairing due to electron-phonon coupling is investigated in recent pump-probe experiments. Combining time-dependent density functional theory and nonadiabatic molecular dynamics, we report the first direct modeling of such experiments and show how the electron-phonon relaxation depends on chemical bonding, electron-phonon coupling, and electronic state density. The relaxation rate is determined primarily by the nonadiabatic charge-phonon coupling strength, which in turn depends on the strength of chemical interactions between the key atoms, reflected in the wave function delocalization. The differences in the electronic density of states constitute the secondary factor. Having obtained good agreement with the experimental data on YBa₂Cu₃O_6.5, we predict that the relaxation slows if Y is replaced with Sc or Ba with Sr, while the relaxation accelerates if O is replaced with S, indicating that YBa₂Cu₃S_6.5 can exhibit improved superconducting performance.