Tracking Cooper Pairs in a Cuprate Superconductor by Ultrafast Angle-Resolved Photoemission

TL;DR

This study investigates the ultrafast dynamics of Cooper pair formation and quasiparticle behavior in a high-temperature cuprate superconductor using time-resolved photoemission and infrared techniques, revealing momentum-dependent recombination processes.

Contribution

It introduces a novel ultrafast spectroscopic approach to directly observe momentum-dependent Cooper pair dynamics in cuprates.

Findings

Superconducting gap dynamics depend on excitation density and momentum.

Near the d-wave nodes, Cooper pairs recombine slowly and are sensitive to pump intensity.

Far from the nodes, recombination is faster and less affected by pumping.

Abstract

In high-temperature superconductivity, the process that leads to the formation of Cooper pairs, the fundamental charge carriers in any superconductor, remains mysterious. We use a femtosecond laser pump pulse to perturb superconducting Bi2Sr2CaCu2O8+{\delta}, and study subsequent dynamics using time- and angle-resolved photoemission and infrared reflectivity probes. Gap and quasiparticle population dynamics reveal marked dependencies on both excitation density and crystal momentum. Close to the d-wave nodes, the superconducting gap is sensitive to the pump intensity and Cooper pairs recombine slowly. Far from the nodes pumping affects the gap only weakly and recombination processes are faster. These results demonstrate a new window into the dynamical processes that govern quasiparticle recombination and gap formation in cuprates.