High-resolution spatial mapping of a superconducting NbN wire using single-electron detection

Superconducting NbN wires have recently received attention as detectors for visible and infrared photons. We present experiments in which we use a NbN wire for high-efficiency (40 %) detection of single electrons with keV energy. We use the beam of a scanning electron microscope as a focussed, stable, and calibrated electron source. Scanning the beam over the surface of the wire provides a map of the detection efficiency. This map shows features as small as 150 nm, revealing wire inhomogeneities. The intrinsic resolution of this mapping method, superior to optical methods, provides the basis of a characterization tool relevant for photon detectors.Comment: 2009 IEEE Toronto International Conference, Science and Technology for Humanity (TIC-STH

Characterization of superconducting multilayers samples

Best RF bulk niobium accelerating cavities have nearly reached their ultimate limits at rf equatorial magnetic field H 200 mT close to the thermodynamic critical field Hc. In 2006 Gurevich proposed to use nanoscale layers of superconducting materials with high values of Hc > HcNb for magnetic shielding of bulk niobium to increase the breakdown magnetic field inside SC RF cavities [1]. Depositing good quality layers inside a whole cavity is rather difficult but we have sputtered high quality samples by applying the technique used for the preparation of superconducting electronics circuits and characterized these samples by X-ray reflectivity, dc resistivity (PPMS) and dc magnetization (SQUID). Dc magnetization curves of a 250 nm thick Nb film have been measured, with and without a magnetron sputtered coating of a single or multiple stack of 15 nm MgO and 25 nm NbN layers. The Nb samples with/without the coating clearly exhibit different behaviors. Because SQUID measurements are influenced by edge and shape effects we propose to develop a specific local magnetic measurement of HC1 based on ac third harmonic analysis in order to reveal the screening effect of multilayers

Dynamics of nonequilibrium quasiparticles in a double superconducting tunnel junction detector

We study a class of superconductive radiation detectors in which the absorption of energy occurs in a long superconductive strip while the redout stage is provided by superconductive tunnel junctions positioned at the two ends of the strip. Such a device is capable both of imaging and energy resolution. In the established current scheme, well studied from the theoretical and experimental point of view, a fundamental ingredient is considered the presence of traps, or regions adjacent to the junctions made of a superconducting material of lower gap. We reconsider the problem by investigating the dynamics of the radiation induced excess quasiparticles in a simpler device, i.e. one without traps. The nonequilibrium excess quasiparticles can be seen to obey a diffusion equation whose coefficients are discontinuous functions of the position. Based on the analytical solution to this equation, we follow the dynamics of the quasiparticles in the device, predict the signal formation of the detector and discuss the potentiality offered by this configuration.Comment: 16 pages, 5 figures Submitted to Superconducting Science and Technolog

Study of nanometric superconducting multilayers for RF field screening applications

Vortex penetration severely limits high field performances in bulk niobium RF cavities for accelerators. To reach higher fields, Gurevich [Appl. Phys. Lett. 88, 012511 (2006)] proposed to deposit nanometric layers (d < λ) to partially screen of the field sensed by niobium. Model (NbN/MgO)n (n = 0 to 4) samples have been deposited on thick Nb layers. This paper presents the first complete characterization set (HC1 and RF surface resistance) of a new family of composite nanostructured superconducting layers deposited on Nb, which are liable to bring a breakthrough in the technology of superconducting accelerating RF cavities

New technology of high Tc superconducting hot electron bolometers for terahertz mixing

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