92 research outputs found
Strong Quasiparticle Trapping In A 6x6 Array Of Vanadium-Aluminum Superconducting Tunnel Junctions
A 6x6 array of symmetrical V/Al/AlOx/Al/V Superconducting Tunnel Junctions
(STJs) was fabricated. The base electrode is a high quality epitaxial film with
a residual resistance ratio (RRR) of ~30. The top film is polycrystalline with
an RRR of ~10. The leakage currents of the 25x25 mm^2 junctions are of the
order of 0.5 pA/mm^2 at a bias voltage of 100 mV, which corresponds to a
dynamical resistance of ~ 3 10^5 ohms. When the array was illuminated by 6 keV
X-ray photons from a 55Fe radioactive source the single photon charge output
was found to be low and strongly dependent on the temperature of the devices.
This temperature dependence at X-ray energies can be explained by the existence
of a very large number of quasiparticle (QP) traps in the Vanadium. QPs are
confined in these traps, having a lower energy gap than the surrounding
material, and are therefore not available for tunneling. The number of traps
can be derived from the energy dependence of the responsivity of the devices
(charge output per electron volt of photon input energy).Comment: 4 pages. presented at Low Temperature Detectors-
Lattice-dynamics of a Disordered solid-solid Interface
Generic properties of elastic phonon transport at a disordered interface are
studied. The results show that phonon transmittance is a strong function of
frequency and the disorder correlation length. At frequencies lower than the
van Hove singularity the transmittance at a given frequency increases as the
correlation length decreases. At low frequencies, this is reflected by
different power-laws for phonon conductance across correlated and uncorrelated
disordered interfaces which are in approximate agreement with perturbation
theory of an elastic continuum. These results can be understood in terms of
simple mosaic and two-colour models of the interface.Comment: 17 pages, 5 figures, submitted to PR
Thin-Film Thermal Conductivity Measurements Using Superconducting Nanowires
We present a simple experimental scheme for estimating the cryogenic thermal transport properties of thin films using superconducting nanowires. In a parallel array of nanowires, the heat from one nanowire in the normal state changes the local temperature around adjacent nanowires, reducing their switching current. Calibration of this change in switching current as a function of bath temperature provides an estimate of the temperature as a function of displacement from the heater. This provides a method of determining the contribution of substrate heat transport to the cooling time of superconducting nanowire single-photon detectors. Understanding this process is necessary for successful electrothermal modeling of superconducting nanowire systems
Optical photon detection in Al Superconducting Tunnel Junctions
We report on the successful fabrication of low leakage aluminium
superconducting tunnel junctions with very homogeneous and transparent
insulating barriers. The junctions were tested in an adiabatic demagnetisation
refrigerator with a base temperature of 35 mK. The normal resistance of the
junctions is equal to ~7 uohm cm2 with leakage currents in the bias voltage
domain as low as 100 fA/um2. Optical single photon counting experiments show a
very high responsivity with charge amplification factors in excess of 100. The
total resolving power (including electronic noise) for 500 nm photons is equal
to 13 compared to a theoretical tunnel limited value of 34. The current devices
are found to be limited spectroscopically by spatial inhomogeneities in the
detectors responseComment: 3 pages, 5 figure
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
Thin-Film Thermal Conductivity Measurements Using Superconducting Nanowires
We present a simple experimental scheme for estimating the cryogenic thermal transport properties of thin films using superconducting nanowires. In a parallel array of nanowires, the heat from one nanowire in the normal state changes the local temperature around adjacent nanowires, reducing their switching current. Calibration of this change in switching current as a function of bath temperature provides an estimate of the temperature as a function of displacement from the heater. This provides a method of determining the contribution of substrate heat transport to the cooling time of superconducting nanowire single-photon detectors. Understanding this process is necessary for successful electrothermal modeling of superconducting nanowire systems
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