Tantalum nitride superconducting single-photon detectors with low   cut-off energy
  Materials with a small superconducting energy gap are expected to favor a high detection efficiency of low-energy photons in superconducting nanowire single-photon detectors. We developed a TaN detector with smaller gap and lower density of states at the Fermi energy than in comparable NbN devices, while other relevant parameters remain essentially unchanged. The observed reduction of the minimum photon energy required for direct detection is in line with model predictions of $\approx1/3$ as compared to NbN. 
Andreas Engel and Adrian Aeschbacher and Kevin Inderbitzin and Andreas   Schilling and Konstantin Il'in and Matthias Hofherr...
cond-mat.supr-con cond-mat.mes-hall