Ultrafast Mid-Infrared Response of YBa_2Cu_3O_(7-δ)

摘要

Optical spectra of high-transition-temperature superconductors in the mid-infrared display a gap of in-plane conductivity whose role for superconductivity remains unresolved. Femtosecond measurements of the mid-infrared reflectivity of YBa_2Cu_3O_(7-δ) after nonequilibrium optical excitation are used to demonstrate the ultrafast fill-in of this gap and reveal two gap constituents: a picosecond recovery of the superconducting condensate in underdoped and optimally doped material and, in underdoped YBa_2Cu_3O_(7-δ), an additional sub-picosecond component related to pseudogap correlations. The temperature-dependent amplitudes of both contributions correlate with the antiferromag-netic 41-millielectronvolt peak in neutron scattering, supporting the coupling between charges and spin excitations.