Role of engineered materials in superconducting tunnel-junction x-ray detectors: suppression of quasi-particle recombination losses via a phononic bandgap

摘要

Abstract: While much progress has been made towards improvedenergy resolution in STJ detectors recently, resultsare still more than an order of magnitude worse thanthe theoretical limit. Several factors have beenidentified as contributing to degradation of energyresolution in STJ devices: recombination losses,parasitic quasiparticle trapping and quasiparticlediffusion into current leads. In addition, STJdetectors tend to have poor photon capture efficiency.Semiconducting detectors achieve their near theoreticalenergy resolutions and high efficiencies via dopingand/or applying an external field to a pure substance.These methods are ineffective for STJ detectors,therefore engineered materials (consisting of multiplematerials artificially patterned on the microscopiclevel) should be considered. The most common engineeredstructures in use are quasiparticle trappingconfigurations which alleviate lead diffusion anddetection efficiency problems, and we have proposed amultilayered approach which addresses parasitictrapping along with diffusion and efficiency. We nowpropose the possibility of a engineered structure whichwill alleviate quasiparticle recombination losses viathe existence of a phononic band gap which overlaps the2$Delta energy of phonons produced during recombinationof quasiparticles. We will present a 1D Kronig-Pennymodel for phonons normally incident to the layers of amultilayered superconducting tunnel junction as anidealized example.!12s