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.
Numerical Simulation of multi-junction bias circuits for superconducting detectors
We present numerical simulations of a new biasing circuit for single photon detectors based on superconducting tunnel junctions. A single detector junction is replaced with a circuit of three junctions to achieve biasing of a detector junction at subgap currents without the use of an external magnetic field. The biasing occurs through the nonlinear interaction of the three junctions. We show nonlinear numerical simulation for different values of junction parameters and demonstrate that the biasing state is numerically stable against external fluctuations. The elimination of the external magnetic field potentially increases the capability of these types of photon detectors and eases constraints involved in the fabrication of large detector arrays.
Quasiparticle trapping from a single-crystal superconductor into a normal-metal film via the proximity effect.
We have studied the dynamics of the nonequilibrium state produced in single-crystal superconducting indium by pulsed laser irradiation using tunnel junctions. By a suitable choice of a thin metal film in intimate contact with the indium crystal, we have been able to produce a pronounced change in the time evolution of the excess quasiparticle density which indicates that the quasiparticles are trapped in the film. This effect can take place both when the film is another superconductor of lower energy gap or is a normal metal made superconducting by the proximity effect.