The characteristic electron–phonon coupling time of unconventional superconductors andimplications for optical detectors

Abstract

Superconductors are highly suitable materials for radiation detection. Several detectortypes have been proposed, with properties of fast detection or high wavelength resolutionover a wide range of optical frequencies. Their performances depend on the relaxationprocesses involving phonons, quasiparticles and Cooper pairs occurring during the energycascade following the absorption of the radiation in the superconductor. The energydown-conversion processes are related to the electron–phonon scattering strengthλe−ph which is usually expressed in terms of the electron–phonon coupling time,τ0, which is characteristic for each material. In this paper we estimate the value ofτ0 for several classes of superconducting materials not yet investigated. It is calculated in theframework of the McMillan model for the superconducting critical temperatureTc within the Debye approximation. The values obtained forτ0 are discussed as regards new possibilities for unexplored materials in the field ofsuperconducting detectors. In particular, we focus our attention on materials withτ0 values that could play a significant role in both hot electron photodetectors andsuperconducting tunnel junction devices.