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In this work we present a study of the dark counts rate in a NbTiN Superconducting Nanowire Single Photon Detectors (SNSPD). We measure the distribution of the time intervals elapsed between two consecutive dark pulses at the fixed temperature of 4,2K. Due to the stochastic nature of the dark counts, the distribution is expected to have a Poisson shape but what we observe is a combination of two Poisson-like processes. A further analysis of the distributions dependence on the bias current highlights that the weight of the two process is not constant. In the scenario presented by Ejrnaes et al. [1], this result can confirm that, in this temperature regime, dark counts are generated mainly by multiple consecutive fluctuation events and the contribution to the dark counts rate coming from single fluctuations increases in the high bias current region.

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 λe−ph which is usually expressed in terms of the electron–phonon coupling time, τ0, which is characteristic for each material. In this paper we estimate the value of τ0 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 τ0 are discussed as regards new possibilities for unexplored materials in the field of superconducting detectors. In particular, we focus our attention on materials with τ0 values that could play a significant role in both hot electron photodetectors and superconducting tunnel junction devices.

The dependence of the critical Josephson current (I-C) and magnetoresistance (MR) on the relative orientation of the ferromagnetic layers is investigated in current perpendicular to plane (CPP) measurements of superconductor/ferromagnetic (S/F) multilayers. Two different CuxNi1-x alloys were chosen so that alternate F-layers reversed at different applied magnetic fields and that the ferromagnetic coherence length was of the order of several nanometres. These structures show a significant CPP high-bias MR, which enables the magnetic state of the devices to be determined directly. We found that I-C is substantially larger when the adjacent F-layers are aligned antiparallel compared to the case of parallel orientation. Since in a pseudo-spin-valve structure the relative F-layer orientation is approximately parallel for zero applied magnetic field, I-C can experience an enhancement when a magnetic field is applied in the plane of the junction. The maximum change of I-C corresponds to the maximum change of MR.

Time-resolved transient pump-probe spectroscopy measurements on proximized ferromagnet/superconductor (F/S) hybrid structures are presented. We focused our attention on both low and high critical temperature superconductors such as Nb and YBCO, while for F the weak-ferromagnetic alloy Ni0.48Cu0.52 has been used. Dynamics of the electron-phonon relaxation process has been investigated as a function of both the temperature and the F-film thickness. In the case of NiCu/Nb bilayers the presence of a thin F overlayer reduces the slow bolometric component of the photoresponse, while in YBCO-based structures faster relaxation times were measured. F/S nanobilayers are very attractive toward the development of novel hybrid superconducting photodetectors.

Photoluminescence spectra of Au/Ag nanoparticles have been investigated experimentally. The clusters were obtained inside an amorphous polymeric matrix by thermal simultaneous decomposition of both gold and silver mercaptides. The optical characterization in terms of photoluminescence showed a red shift of position of the emission peak as a function of the Ag mercaptide concentration. The red shift is qualitatively explained in terms of the Jellium model along with the quantum size effects.

Superconducting Tunnel Junctions are promising devices in next generation nuclear and optical detectors. Unfortunately, a number of relaxation processes in the number of initially produced excitations degrades the performances of such devices. In order to investigate the role of charge loss mechanisms in Nb and/or at the Nb/Si interface we have fabricated three terminal in-plane double tunnel junctions, in which quasi-particles are injected into a Nb common strip and detected at different distances by tunnel junctions. The detection efficiency η decreases of about one order of magnitude from T=4.2K to T=1.2K for any injector-detector distance. The presence of charge trapping centers, activated at low temperatures, can qualitatively explain such a result. The estimation of the quasi-particle diffusion constant D=28±5 cm2/s at T=1.2 K is in agreement with other similar values reported in literature.