Theory of ultrafast quasiparticle dynamics in high-temperature superconductors: Pump fluence dependence

TL;DR

This paper develops a theoretical model for ultrafast quasiparticle dynamics in high-temperature superconductors, revealing how anisotropic electron-phonon interactions influence optical responses and exhibit re-entrant behavior related to the superconducting state.

Contribution

It introduces a theory capturing the pump fluence dependence of quasiparticle dynamics, highlighting anisotropic electron-phonon coupling effects in high-Tc superconductors.

Findings

Higher-energy peak in optical spectra linked to B1g phonon mode

No strong coupling observed for Cu-O breathing mode

Re-entrant behavior of spectral signature correlates with superconducting condensate

Abstract

We present a theory for the time-resolved optical spectroscopy of high-temperature superconductors at high excitation densities with strongly anisotropic electron-phonon coupling. A signature of the strong coupling between the out-of-plane, out-of-phase O buckling mode ($B_{1g}$) and electronic states near the antinode is observed as a higher-energy peak in the time-resolved optical conductivity and Raman spectra, while no evidence of the strong coupling between the in-plane Cu-O breathing mode and nodal electronic states is observed. More interestingly, it is observed that under appropriate conditions of pump fluence, this signature exhibits a re-entrant behavior with time delay, following the fate of the superconducting condensate.