Optical photon detection in Al superconducting tunnel junctions

Abstract

We report on the successful fabrication of low leakage aluminium superconducting tunnel junctions with very homogeneous and transparent insulating barriers. The junctions were tested in an adiabatic demagnetisation refrigerator with a base temperature of 35 mK. The normal resistance of the junctions is equal to ~7 µΩ cm 2 with leakage currents in the bias voltage domain as low as 100 fA/µm 2 . Optical single photon counting experiments show a very high responsivity with charge amplification factors in excess of 100. The total resolving power λ/∆λ (including electronic noise) for 500 nm photons is equal to 13 compared to a theoretical tunnel limited value of 34. The current devices are found to be limited spectroscopically by spatial inhomogeneities in the detectors response

The characteristic electron–phonon coupling time of unconventional superconductors and implications for optical detectors

“…However, the performances were not sufficiently competitive in comparison with lower gap materials. Recently, V and Mo have been explored [42]. Good V-based STJs have been fabricated.…”

Local thermal fluctuations in current-carrying superconducting nanowires

“…For ∆ = 2.05 k B T c and the photon energy 1 eV we obtain σ E ≈ 7 meV, which is also much less than our experimental values. Even if one takes experimental values for energy resolution of superconducting tunnel-junction detectors [31,32] which is believed to be fundamentally limited by Fano fluctuations, corresponding standard deviation will be two to three times larger than our estimate of the Fano variance. Effect of the film granularity is hard to address quantitatively.…”