Photoinduced time-resolved electrodynamics of superconducting metals and alloys

TL;DR

This study investigates the ultrafast dynamics of superconducting metals and alloys using pump-probe spectroscopy, revealing how photoexcitation affects the superconducting gap and relaxation processes.

Contribution

It provides the first detailed time- and frequency-resolved measurements of photoinduced effects in various superconducting thin films, elucidating relaxation mechanisms.

Findings

Identified phonon bottleneck and quasiparticle recombination regimes.

Measured reduction of superconducting gap after photoexcitation.

Established temperature limits for low-fluence approximation.

Abstract

The photoexcited state in superconducting metals and alloys was studied via pump-probe spectroscopy. A pulsed Ti:sapphire laser was used to create the non-equilibrium state and the far-infrared pulses of a synchrotron storage ring, to which the laser is synchronized, measured the changes in the material optical properties. Both the time- and frequency- dependent photoinduced spectra of Pb, Nb, NbN, Nb{0.5}Ti{0.5}N, and Pb{0.75}Bi{0.25} superconducting thin films were measured in the low-fluence regime. The time dependent data establish the regions where the relaxation rate is dominated either by the phonon escape time (phonon bottleneck effect) or by the intrinsic quasiparticle recombination time. The photoinduced spectra measure directly the reduction of the superconducting gap due to an excess number of quasiparticles created by the short laser pulses. This gap shift allows us to establish the temperature range over which the low fluence approximation is valid.