Superconducting NbTaAlAlOxAl X-ray detectors with spatial resolution
Abstract Superconducting X-ray detectors based on SIS tunnel junctions offer potential for high spectral resolution and single photon efficiency. When used in a double junction geometry, they also offer spatial resolution needed for focal plane imaging. We are developing NbTaAlAlOxAl detectors for space-based X-ray astronomy applications. The design employs superconductor bandgap engineering for improved charge collection and adaptability for double junction geometries. For irradiation of a single junction device with 6 keV X-rays at a single location, the detectors have an energy resolution of 87 eV at 0.27 K. Initial studies of double junction detectors show a spectral resolution of 178 eV and an inferred spatial resolution of 4 μm over an effective length of 60 μm.
High-resolution superconducting X-ray spectrometers with an active area of 282 /spl mu/m/spl times/282 /spl mu/m
Superconducting tunnel junctions coupled to superconducting absorbers may be used as high-resolution, high-efficiency X-ray spectrometers. We have tested devices with niobium X-ray absorbing layers coupled to aluminum layers that serve as quasiparticle traps. In this work we measure the current pulses from a large-area tunnel junction using an amplifier based on an array of 100 SQUIDs. Using this amplifier and a 282 /spl mu/m/spl times/282 /spl mu/m junction, we have measured an energy resolution of 19 eV FWHM for 1.5 keV X-rays and 21 eV for 2.6 keV X-rays. The area of this junction is eight times the area of any junction previously measured to have such high energy resolution.
Steady state measurements of the quasiparticle lifetime in superconducting aluminium
We report details of the steady state measurements of the quasiparticle lifetime (τ) in superconducting aluminium which were published previously. We begin with a synopsis of the relevant background, followed by an explanation of our experimental procedure. Included are some aspects of the experiments not primarily related to the lifetime measurements. It is shown that the process responsible for the excess current found by Burstein and Taylor in aluminium tunnel junctions for Δ 4Δ we observe enhanced injection of quasiparticles. We show that the effect of heating on the lifetime measurements is negligible at low temperatures and can be accounted for near the transition temperature (Tc). Near Tc there is another recombination process in which the excess energy is absorbed by another quasiparticle. Very near Tc there are indications that τ becomes very long. As the temperature decreases much below Tc, τ approaches a constant value due to recombination in regions of flux penetration.