The characteristic electron-phonon coupling time of unconventional superconductors and implications for optical detectors

Superconductors are highly suitable materials for radiation detection. Several detector types have been proposed, with properties of fast detection or high wavelength resolution over a wide range of optical frequencies. Their performances depend on the relaxation processes involving phonons, quasiparticles and Cooper pairs occurring during the energy cascade following the absorption of the radiation in the superconductor. The energy down-conversion processes are related to the electron-phonon scattering strength ?e-ph which is usually expressed in terms of the electron-phonon coupling time, ?0, which is characteristic for each material. In this paper we estimate the value of ?0 for several classes of superconducting materials not yet investigated. It is calculated in the framework of the McMillan model for the superconducting critical temperature Tc within the Debye approximation. The values obtained for ?0 are discussed as regards new possibilities for unexplored materials in the field of superconducting detectors. In particular, we focus our attention on materials with ?0 values that could play a significant role in both hot electron photodetectors and superconducting tunnel junction devices.