17 research outputs found
Advanced code-division multiplexers for superconducting detector arrays
Multiplexers based on the modulation of superconducting quantum interference
devices are now regularly used in multi-kilopixel arrays of superconducting
detectors for astrophysics, cosmology, and materials analysis. Over the next
decade, much larger arrays will be needed. These larger arrays require new
modulation techniques and compact multiplexer elements that fit within each
pixel. We present a new in-focal-plane code-division multiplexer that provides
multiplexing elements with the required scalability. This code-division
multiplexer uses compact lithographic modulation elements that simultaneously
multiplex both signal outputs and superconducting transition-edge sensor (TES)
detector bias voltages. It eliminates the shunt resistor used to voltage bias
TES detectors, greatly reduces power dissipation, allows different dc bias
voltages for each TES, and makes all elements sufficiently compact to fit
inside the detector pixel area. These in-focal-plane code-division multiplexers
can be combined with multi-gigahertz readout based on superconducting
microresonators to scale to even larger arrays.Comment: 8 pages, 3 figures, presented at the 14th International Workshop on
Low Temperature Detectors, Heidelberg University, August 1-5, 2011,
proceedings to be published in the Journal of Low Temperature Physic
Quantum superconductor-metal transition
We consider a system of superconducting grains embedded in a normal metal. At
zero temperature this system exhibits a quantum superconductor-normal metal
phase transition. This transition can take place at arbitrarily large
conductance of the normal metal.Comment: 13 pages, 1 figure include
Crossover and scaling in a two-dimensional field-tuned superconductor
Using an analysis similar to that of Imry and Wortis, it is shown that the
apparent first order superconductor to metal transition, which has been claimed
to exist at low values of the magnetic field in a two-dimensional field-tuned
system at zero temperature,can be consistentlyinterpreted as a sharp crossover
from a strong superconductor to an inhomogeneous state, which is a weak
superconductor. The true zero-temperature superconductor to insulator
transition within the inhomogenous state is conjectured to be that of randomly
diluted XY model. An explaination of the observed finite temperature
approximate scaling of resistivity close to the critical point is speculated
within this model.Comment: 5 pages, 2 figures, corrected and modified according to referee
Report
The Upper Critical Field in Disordered Two-Dimensional Superconductors
We present calculations of the upper critical field in superconducting films
as a function of increasing disorder (as measured by the normal state
resistance per square). In contradiction to previous work, we find that there
is no anomalous low-temperature positive curvature in the upper critical field
as disorder is increased. We show that the previous prediction of this effect
is due to an unjustified analytical approximation of sums occuring in the
perturbative calculation. Our treatment includes both a careful analysis of
first-order perturbation theory, and a non-perturbative resummation technique.
No anomalous curvature is found in either case. We present our results in
graphical form.Comment: 11 pages, 8 figure
True Superconductivity in a 2D "Superconducting-Insulating" System
We present results on disordered amorphous films which are expected to
undergo a field-tuned Superconductor-Insulator Transition. Based on low-field
data and I-V characteristics, we find evidence of a low temperature
Metal-to-Superconductor transition. This transition is characterized by
hysteretic magnetoresistance and discontinuities in the I-V curves. The
metallic phase just above the transition is different from the "Fermi Metal"
before superconductivity sets in.Comment: 3 pages, 4 figure
Effect of Magnetic Impurities on Suppression of the Transition Temperature in Disordered Superconductors
We calculate the first-order perturbative correction to the transition
temperature in a superconductor with both non-magnetic and magnetic
impurities. We do this by first evaluating the correction to the effective
potential, , and then obtain the first-order correction to the
order parameter, , by finding the minimum of . Setting
finally allows to be evaluated. is now a function of
both the resistance per square, , a measure of the non-magnetic
disorder, and the spin-flip scattering rate, , a measure of the
magnetic disorder. We find that the effective pair-breaking rate per magnetic
impurity is virtually independent of the resistance per square of the film, in
agreement with an experiment of Chervenak and Valles. This conclusion is
supported by both the perturbative calculation, and by a non-perturbative
re-summation technique.Comment: 29 pages, 9 figure
Vortex dynamics and upper critical fields in ultrathin Bi films
Current-voltage (I-V) characteristics of quench condensed, superconducting,
ultrathin films in a magnetic field are reported. These I-V's show
hysteresis for all films, grown both with and without thin underlayers.
Films on Ge underlayers, close to superconductor-insulator transition (SIT),
show a peak in the critical current, indicating a structural transformation of
the vortex solid (VS). These underlayers, used to make the films more
homogeneous, are found to be more effective in pinning the vortices. The upper
critical fields (B) of these films are determined from the resistive
transitions in perpendicular magnetic field. The temperature dependence of the
upper critical field is found to differ significantly from Ginzburg-Landau
theory, after modifications for disorder.Comment: Phys Rev B, to be published Figure 6 replaced with correct figur
Design of the detection chain for Athena X-IFU
International audienceThe x-ray integral field unit (X-IFU) instrument is the high-resolution x-ray spectrometer of the ESA Athena x-ray observatory. X-IFU will deliver spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV from 5" pixels, with a hexagonal field of view of 5' equivalent diameter. The main sensor array and its associated detection chain is one of the major sub-systems of the X-IFU instrument, and is the main contributor to X-IFU’s performance. CNES (the French Space Agency) is leading the development of X-IFU; additional major partners are NASA-GFSC, SRON, VTT, APC, NIST, and IRAP. This paper updates the B-phase definition of the X-IFU detection chain. The readout is based on time-division multiplexing (TDM). The different sub-components of the detection chain (the main sensor array, the cold electronics stages, and the warm electronics) require global design optimization in order to achieve the best performance. The detection chain’s sensitivity to the EMI/EMC environment requires detailed analysis and implementation of dedicated design solutions. This paper focuses on these aspects while providing an update to the detection-chain design description. © COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only