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.
@article{arxiv.1206.2300,
title = {Tracking Cooper Pairs in a Cuprate Superconductor by Ultrafast Angle-Resolved Photoemission},
author = {Christopher L. Smallwood and James P. Hinton and Christopher Jozwiak and Wentao Zhang and Jake D. Koralek and Hiroshi Eisaki and Dung-Hai Lee and Joseph Orenstein and Alessandra Lanzara},
journal= {arXiv preprint arXiv:1206.2300},
year = {2012}
}