Single photon detection in NbRe superconducting microstrips

Abstract

Detection of single infrared photons in superconducting microstrips of 4 nm thick disordered Nb0.15Re0.85 has been investigated. Microstrips with a critical temperature of 5.15 K and widths from 1.0 to 2.5  μm have been fabricated by optical lithography. We demonstrate single photon detection sensitivity at 1.5  μm wavelength at a temperature of 1.79 K. By investigating the detection process at this temperature, we find that the current bias threshold is at 21% of the depairing current. This threshold is similar to what should be observed in typical amorphous superconductors, which confirms that ultrathin disordered Nb0.15Re0.85 is an interesting material for superconducting microstrip single photon detectors that operate above 1 K.