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Estimation of the relaxation time in NbReN microstrips of different widths for superconducting single photon detectors.
Makhdoumi Kakhaki Z., Leo A., Ejrnaes M., Parlato L., Nigro A., Pepe G.P., Cirillo C., Attanasio C.
Recently, superconducting microstrips have been proposed as single-photon detectors as an alternative to more sophisticated nanowire structures. In this work, we fabricated by ultra-high vacuum DC magnetron sputtering microstrips of NbReN, a promising material for single-photon detection. We study the nonequilibrium state generated by vortex motion in microstrips with thickness of about 10 nm and widths, $w$, between 2 and 10 $\mu$m. In particular, by analysing the shape of the I-V curves in the flux-flow regime and the dependence of the critical current on the magnetic field we obtain indication on the main pinning mechanisms (edge barrier or bulk pinning) present in the films. Moreover, from the investigation of the instability in the I-V curves, we estimate the vortex critical velocity, $\upsilon^*$, and the quasi-particles relaxation time, $\tau$. The values of these two parameters give further indication of the dominant pinning mechanism. The small value of $\tau$ (about 300 ps) obtained for $w=10 \mu$m further suggests the potential of NbReN for the realization of superconducting single-photon detectors with large areas obtained by low-cost fabrication techniques.