Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy

TL;DR

This study uses time-resolved terahertz spectroscopy to investigate how the superconducting energy gap in NbN thin films is suppressed and recovers after photoexcitation, revealing detailed dynamics and key physical parameters.

Contribution

It provides the first direct measurement of quasiparticle recombination and pair-breaking rates in NbN, validating the Rothwarf-Taylor model and determining the electron-phonon coupling constant.

Findings

Recombination rate and pair-breaking rate are temperature and excitation dependent.

Electron-phonon coupling constant bb = 1.1 1 matches theoretical predictions.

Superconducting gap dynamics follow Rothwarf-Taylor model predictions.

Abstract

Using time-domain Terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, \lambda = 1.1 +/- 0.1, which is in excellent agreement with theoretical estimates.