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Hotspot Relaxation Dynamics in a Current Carrying Superconductor



Francesco Marsili, Martin Stevens, Alex Kozorezov, Varun Verma, Colin Lambert, Jeffrey A. Stern, Rob Horansky, Shellee D. Dyer, Shannon Duff, David P. Pappas, Matthew Shaw, Richard Mirin, Sae Woo Nam


When a photon is absorbed in a superconductor it creates a region of nonequilibrium superconductivity referred to as a hotspot [1]. The operation of most superconducting single photon detectors (microwave kinetic inductance detectors, MKIDs [2,3], superconducting tunnel junctions, STJs [4], and superconducting nanowire single photon detectors, SNSPDs [5]) is based on the hotspot effect in thin superconducting films. After several decades of research in the field of optically excited superconductors, there remain open questions about the details of hotspot formation and relaxation. Here we report measurements of the relaxation time of hotspots excited by single photons in current carrying WSi superconducting nanowires. We observed two effects for the first time: (1) the hotspot relaxation time (tHS) depends on the current carried by the superconducting nanowires; and (2) the current dependence of tHS changes with temperature and wavelength. We have developed a model that accounts for both effects. In addition to shedding new light on the photodetection mechanism in SNSPDs, STJs, and MKIDs, our model can provide a deeper insight into quasiparticle dynamics in superconductors.
Physical Review B


single photon detectors, superconductivity


Marsili, F. , Stevens, M. , Kozorezov, A. , Verma, V. , Lambert, C. , Stern, J. , Horansky, R. , Dyer, S. , Duff, S. , Pappas, D. , Shaw, M. , Mirin, R. and Nam, S. (2016), Hotspot Relaxation Dynamics in a Current Carrying Superconductor, Physical Review B, [online],, (Accessed December 8, 2023)
Created March 16, 2016, Updated October 12, 2021