Nonequilibrium Pair Breaking in $\mathrm{Ba}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}{\mathrm{As}}_{2}$ Superconductors: Evidence for Formation of a Photoinduced Excitonic State

Nonequilibrium Pair Breaking in $Ba ({Fe}_{1 - x} {Co}_{x})_{2} {As}_{2}$ Superconductors: Evidence for Formation of a Photoinduced Excitonic State

X. Yang, L. Luo, M. Mootz, A. Patz, S. L. Bud’ko, P. C. Canfield, I. E. Perakis, and J. Wang

Phys. Rev. Lett. 121, 267001 – Published 26 December 2018

Abstract

Ultrafast terahertz (THz) pump-probe spectroscopy reveals an unusual out-of-equilibrium Cooper pair nonlinear dynamics and a nonequilibrium state driven by femtosecond (fs) photoexcitation of superconductivity (SC) in iron pnictides. Following fast SC quench via hot-phonon scattering, a second, abnormally slow (many hundreds of picoseconds), SC quench regime is observed prior to any recovery. Importantly, a nonlinear pump fluence dependence is identified for this remarkably long prebottleneck dynamics that are sensitive to both doping and temperature. Using quantum kinetic modeling we argue that the buildup of excitonic interpocket correlation between electron-hole ( $e − h$ ) quasiparticles (QP) quenches SC after fs photoexcitation leading to a long-lived, many-QP excitonic state.

Received 3 April 2018
Revised 11 July 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.267001

Physics Subject Headings (PhySH)

Superconductivity

Iron-based superconductors Pnictides

Femtosecond laser spectroscopy Terahertz spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

X. Yang¹, L. Luo¹, M. Mootz², A. Patz¹, S. L. Bud’ko¹, P. C. Canfield¹, I. E. Perakis², and J. Wang¹

¹Department of Physics and Astronomy and Ames Laboratory-U.S. DOE, Iowa State University, Ames, Iowa 50011, USA
²Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35294-1170, USA