Characteristics of superconducting tungsten silicide WxSi1−x for single photon detection

Abstract

Superconducting properties of three series of amorphous W x Si 1x films with different thickness and stoichiometry were investigated by dc transport measurements in a magnetic field up to 9 T. These amorphous W x Si 1x films were deposited by magnetron cosputtering of the elemental source targets onto silicon substrates at room temperature and patterned in the form of bridges by optical lithography and reactive ion etching. Analysis of the data on magnetoconductivity allowed us to extract the critical temperatures, superconducting coherence lengths, magnetic penetration depths, and diffusion constants of electrons in the normal state as functions of film thickness for each stoichiometry. Two basic time constants were derived from transport and time-resolving measurements. A dynamic process of the formation of a hotspot was analyzed in the framework of a diffusion-based vortex-entry model. We used a two-stage diffusion approach and defined a hotspot size by assuming that the quasiparticles and normal-state electrons have the same diffusion constant. With this definition and these measured material parameters, the hotspot in the 5-nm-thick W 0.85 Si 0.15 film had a diameter of 107 nm at the peak of the number of nonequilibrium quasiparticles. Superconducting properties of three series of amorphous W x Si 1−x films with different thickness and stoichiometry were investigated by dc transport measurements in a magnetic field up to 9 T. These amorphous W x Si 1−x films were deposited by magnetron cosputtering of the elemental source targets onto silicon substrates at room temperature and patterned in the form of bridges by optical lithography and reactive ion etching. Analysis of the data on magnetoconductivity allowed us to extract the critical temperatures, superconducting coherence lengths, magnetic penetration depths, and diffusion constants of electrons in the normal state as functions of film thickness for each stoichiometry. Two basic time constants were derived from transport and time-resolving measurements. A dynamic process of the formation of a hotspot was analyzed in the framework of a diffusion-based vortex-entry model. We used a two-stage diffusion approach and defined a hotspot size by assuming that the quasiparticles and normal-state electrons have the same diffusion constant. With this definition and these measured material parameters, the hotspot in the 5-nm-thick W 0.85 Si 0.15 film had a diameter of 107 nm at the peak of the number of nonequilibrium quasiparticles.

Electronic and phononic properties of a two-dimensional electron gas coupled to dipolar phonons via small-momentum-transfer scattering

“…Due to the strong small-momentum electron-phonon interaction it is argued that the linewidth of smallmomentum phonon should be large. However, this expectation is inconsistent with recent electron energy loss spectroscopy [20,54]. This fact has been used to question the validity of the attribution of the replica band to the near-forward electron-phonon interaction [20].…”

Tracing Monopoles and Anti-monopoles in a Magnetic Hedgehog Lattice

“…Our results also explicitly show that how their trajectories are related with the uniform scalar spin chirality and the fictitious fluxes. One of the differences from the predictions by the continuum approximation [6] is that the monopoles and anti-monopoles do not collide with each other but are repelled by other monopoles and antimonopoles before pair annihilations. This suggests the existence of repulsive interactions between the monopoles and anti-monopoles coming from different layers, when the spin textures are optimized on the discrete lattice during the field sweep.…”

“…Note that the pair shown in the Fig. 3(c) corresponds to (5,6). When increasing the magnetic field, the (anti-)monopoles move to the upper (lower) layers, while they move in the xy directions as well, as shown in Fig.…”

“…Figure 5 shows the trajectories of the monopoles and anti-monopoles in this field sweep, drawn by tracing the positions where Q m = ±1. At h = 0, there are four pairs of monopoles and anti-monopoles, (1,2), (3,4), (5,6), and (7,8), on the xy planes with z = 2.5, 8.5, 14.5, and 20.5, respectively, as shown in Fig. 5(a).…”

“…(c) indicates that the hedgehog and anti-hedgehog are a monopole and anti-monopole of the effective field, respectively. mation, and the shift, collision, and pair annihilation were predicted while increasing the field [6]. In MnGe, however, the 3Q-HL has a very short period of ∼ 3 nm, which is far from the continuum limit.…”