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

Abstract

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

Influence of the magnetic configuration on the vortex-lattice instability in Nb/permalloy bilayers

“…When the bias current is further increased, the linear flux-flow regime is present until a certain value I * , where a sudden jump of the voltage V * takes place in agreement with the Larkin-Ovchinnikov theory [9]. Such instabilities were previously observed in a number of different superconducting systems [1,6,7,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. V * is related to the so-called critical velocity v * by the relation [9] At high fields the jump is replaced by a more continuous transition towards the normal state, as is clearly seen looking at the curves corresponding to the fields of 0.4 and 0.5 T in the inset of Fig.…”

“…In contrast, in the case of S/F hybrids a thin F layer will be completely proximized so that different superconducting properties appear at a distance of the order of α. Moreover, by studying the dynamic properties of the vortex lattice in S/F structures, it was found that the performance of the detecting devices in terms of the quasiparticle relaxation rates seems to be strongly enhanced by the presence of the F layer [1,2,[6][7][8]. In particular, from the analysis of the critical velocity v * for the occurrence of the instability of the moving vortex lattice [9], information on the quasiparticle relaxation time τ E was obtained, and it was shown that in order to reduce the values of τ E it is useful to couple the superconductor to a strong ferromagnet, such as permalloy [2].…”

“…Gaining knowledge of the vortex lattice instability and nonequilibrium superconductivity in superconducting/ferromagnetic (S/F) systems is crucial in the design of S/F-based devices [1,2]. For example, it was experimentally proved that S/F hybrids are optimal systems to be used as ultrafast superconducting optical detectors and eventually even as single photon detectors, due to the small value of the penetration length of the superconducting correlations in the F layer, ξ F 6 nm, which determines better performance in terms of both photoresponse signal detection and sensitivity [3][4][5].…”

Photon-triggered instability in the flux flow regime of a strongly disordered superconducting strip

“…Here, we propose that single-photon response can occur also in a superconducting strip in which vortices are present induced by a perpendicular magnetic field. In such films, an applied current induces a resistive flux flow state, which transits into a more resistive state at a "quench" current I q (H ) > I c (H ) [5][6][7][8][9][10][11][12][13][14][15][16]. The critical current I c (H ) is magnetic field dependent, because it controls the density of vortices.…”

Investigation of dark counts in innovative materials for superconducting nanowire single-photon detector applications

“…Within this idea, we have investigated the phenomenon of dark counts in nanostripes based on high-T C superconducting YBa 2 Cu 3 O 7-x (YBCO) and superconductor/ferromagnet NbN/NiCu and YBa 2 Cu 3 O 7-x /L 0.7 Sr 0.3 MnO 3 (YBCO/LSMO) hybrids. In the case of hybrid structures, our previous studies have shown that the presence of an ultrathin ferromagnetic overlayer influences the superconducting properties of the bilayer, in terms of the critical current density J C , T C , as well as the electron relaxation time [13][14][15][16]. In work presented here, we focus on dark-count measurements in hybrid, superconductor/ferromagnet (S/F) stripes patterned from nanobilayers consisting of ultrathin NiCu weak ferromagnetic films deposited top of ultrathin NbN films, as well as from pure NbN films fabricated in the same conditions and treated as a reference.…”