Ultrafast decoupling of quasiparticles and spin fluctuations in superconducting cuprates
Abstract
Understanding how quasiparticles are generated following a rapid quench of superconductivity in high-Tc cuprates is a key unresolved problem in nonequilibrium superconductivity. Here we resolve these processes in optimally doped YBCO [YBa2Cu3Oy(y=6.94, Tc=92 K)] using broadband (0.16 -4.1 eV, ca. 100 fs) and nearly single-cycle (6 fs) transient reflectivity spectroscopy. We show that within a few femtosecond, enhanced electron-electron Umklapp scattering dominates, signaling a transient modulation of long-range Coulomb interactions on the eV scale. This regime is followed by a rapid suppression of the scattering rate of the mid-infrared absorption associated with carriers dressed by spin fluctuations. We attribute this observation to an ultrafast decoupling of quasiparticles from the spin-fluctuation background, occurring on a 90 fs timescale set by the inverse optical gap. These findings reveal the correlated many-body dynamics underlying quasiparticle generation in cuprates and provide further clues for unconventional pairing mechanism.
Keywords
Cite
@article{arxiv.2605.14238,
title = {Ultrafast decoupling of quasiparticles and spin fluctuations in superconducting cuprates},
author = {Yuto Taniguchi and Ryo Kato and Tatsuya Amano and Hirotake Itoh and Yohei Kawakam and Yuto Nakamura and Hideo Kishida and Christian Bernhard and Jure Demsar and Takahiko Sasaki and Terukazu Nishizaki and Kenji Yonemitsu and Shinichiro Iwai},
journal= {arXiv preprint arXiv:2605.14238},
year = {2026}
}
Comments
24 pages , 5 figure (main text) and 14 pages (supplemental material)