Nonequilibrium superconducting thin films with sub-gap and pair-breaking photon illumination

Abstract

We calculate nonequilibrium quasiparticle and phonon distributions for a number of widely-used low transition temperature thin-film superconductors under constant, uniform illumination by sub-gap probe and pair-breaking signal photons simultaneously. From these distributions we calculate material-characteristic parameters that allow rapid evaluation of an effective quasiparticle temperature using a simple analytical expression, for all materials studied (Mo, Al, Ta, Nb, and NbN) for all photon energies. We also explore the temperature and energy-dependence of the low-energy quasiparticle generation efficiency $\eta$ by pair-breaking signal photons finding $\eta \approx 0.6$ in the limit of thick films at low bath temperatures that is material-independent. Taking the energy distribution of excess quasiparticles into account, we find $\eta \to 1$ as the bath temperature approaches the transition temperature in agreement with the assumption of the two-temperature model of the nonequilibrium response that is appropriate in that regime. The behaviour of $\eta$ with signal frequency scaled by the superconducting energy gap is also shown to be material-independent, and is in qualitative agreement with recent experimental results. An enhancement of $\eta$ in the presence of sub-gap (probe) photons is shown to be most significant at signal frequencies near the superconducting gap frequency and arises due to multiple photon absorption events that increase the average energy of excess quasiparticles above that in the absence of the probe.

arXiv comment9 pages, 7 figures

References in corpus (6)

• Preparation and Measurement of Three-Qubit Entanglement in a Superconducting Circuit
• Evidence of a nonequilibrium distribution of quasiparticles in the microwave response of a superconducting aluminium resonator
• Fluctuations in the electron system of a superconductor exposed to a photon flux
• Quasiparticle generation efficiency in superconducting thin-films
• Microwave-induced excess quasiparticles in superconducting resonators measured through correlated conductivity fluctuations
• Non-equilibrium superconductivity in superconducting resonators

Cited by in corpus (14)

• A kilo-pixel imaging system for future space based far-infrared observatories using microwave kinetic inductance detectors
• Josephson-junction infrared single-photon detector
• Design and Characterization of a Phonon-Mediated Cryogenic Particle Detector with an eV-Scale Threshold and 100 keV-Scale Dynamic Range
• Nonlinear Effects in Superconducting Thin Film Microwave Resonators
• The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band
• Tuning critical field, critical current, and diode effect of narrow thin-film superconductors through engineering inhomogeneous Pearl length
• Nonequilibrium quasiparticle distribution in superconducting resonators: effect of pair-breaking photons
• Nonlinear mechanisms in Al and Ti superconducting travelling-wave parametric amplifiers
• Anomalous Loss Reduction Below Two-Level System Saturation in Aluminum Superconducting Resonators
• Power and temperature dependent model for High Q superconductors
• Electrothermal Feedback in Kinetic Inductance Detectors
• Broadband illumination of superconducting pair breaking photon detectors
• Study of quasi-particle dynamics using the optical pulse response of asuperconducting resonator
• Volume dependence of microwave induced excess quasiparticles in superconducting resonators