X-ray photon detection with multilayered Josephson junctions

Superconducting tunnel junctions can be configured as high resolution X-ray spectrometers however, because they are thin, STJs suffer from inherent photoabsorption inefficiency. A common approach to enhance quantum efficiency is to couple the junctions to superconducting absorbers and employ quasiparticle traps. An alternative approach is to use vertical stacks of tunnel junctions as detectors. These multilayered superconducting tunnel junctions (MSTJs) need not be thin and may have additional advantages including increased signal to noise ratio. We report on the fabrication of multilayered tunnel junctions and successful X-ray detection by an MSTJ.