Quasiparticles energy relaxation times in NbN/CuNi nanostripes from critical velocity measurements

The dynamic instability of the moving vortex lattice at high driving currents in NbN/CuNi-based and NbN nanostripes designed for optical detection has been studied. By applying the model proposed by Larkin and Ovchinnikov [Zh. Eksp. Teor. Fiz. 68, 1915 (1975)], from the critical velocity v∗ for the occurrence of the instability, it was possible to estimate the values of the quasiparticle relaxation times τE. The results show that the NbN/CuNi-based devices are characterized by shorter values of τE compared to that of NbN

Investigation of Dark Counts in Innovative Materials for Superconducting Nanowire Single-photon Detector Applications

The phenomenon of dark counts in nanostripes of different superconductor systems such as high-temperature superconducting YBa2Cu3O7-x and superconductor/ferromagnet hybrids consisting of either NbN/NiCu or YBa2Cu3O7- x/L0.7Sr0.3MnO3 bilayers have been investigated. For NbN/NiCu the rate of dark-count transients have been reduced with respect to pure NbN nanostripes and the events were dominated by a single vortex entry from the edge of the stripe. In the case of nanostripes based on YBa2Cu3O7-x, we have found that thermal activation of vortices was also, apparently, responsible for triggering dark-count signals

Terahertz response of high-Tc ramp-type junctions on MgO

We successfully fabricated the high-T-c ramp-type junctions with PrBa2Cu3-xGaxO7-delta (PBCGO:x=0.1, 0.4) barriers on MgO substrates. The junctions showed RSJ-like I-V curves with increased thermally and voltage activated conductivity. The IcRn products for these junctions scale very well with the Ga-doping. Using far infrared laser radiations, we confirmed terahertz (THz) responses of these junctions. The junction with PBCGO (x=0.4) had IcRn products of similar to 1mV at 4.2K and showed Shapiro steps with THz-wave irradiation, without any additional antenna structure

Performance of Superconducting Single-Photon Detectors Using NbN/NiCu Nanowires

We present optical properties of nanowires consisting of both proximitized superconductor/ferromagnet bilayers of NbN/NiCu and pure superconducting NbN layers. Thin NbN/NiCu hetero-structures were deposited on MgO(100) substrates by in situ dc magnetron sputtering, while nanowires were patterned using standard electron beam lithography and reactive ion etching. Photo-response signals were recorded from 100-nm-wide, three-parallel and six-series NbN(8 nm)/NiCu nanowires by 850-nm pulsed laser irradiation (time width 400 ps, repetition rate ∼100 MHz). For the latter configuration the fall time of voltage responses was found to be close to 1.7 ns, and it gradually increased with increasing the NiCu film thickness. Moreover, three discrete families of photo-response signals recorded for the three-parallel and six-series nanowires were also observed