Anomalous temperature and galvanomagnetic effects in a niobium-based superconducting tunnel junction

We report transport and phonon pulse experiments carried out to investigate the processes responsible for excess currents in superconducting tunnel junction (STJ) photon detectors. In an edge-anodised niobium device below 1.5 K anomalous temperature and galvano-magnetic effects were observed which correlated also to an increase in device responsivity, but with no significant change in loss rate, as determined by phonon pulses. The observations cannot be accounted for by any simple defect model and may be caused by the creation of a non-equilibrium qp stationary state.