Subharmonic energy-gap structure and heating effects in superconducting niobium point contacts

We present experimental data of the temperature-dependent subharmonic energy-gap structure (SGS) in the current-voltage (I-V) curves of superconducting niobium point contacts. The observed SGS is modified by heating effects. We construct a model of the quasiparticle conductance of metallic superconducting weak links that includes the heating effects self-consistently. Our model is combined with that of Octavio, Blonder, Klapwijk, and Tinkham [Phys. Rev. B 27, 6739 (1983)], which is based on the idea of multiple Andreev scattering in the contact. The shape and the temperature variation of the calculated SGS is found to be in good agreement with the experimental curves for contacts with resistance larger than 5 Ω

Some characteristics of Josephson junctions as radiation detectors

The V-I characteristic of Josephson junction with an external parallel admittance, the high frequency impedance and high frequency response of a Josephson junction to small external signal are calculated by analytical method. The experimentally obtained spectral response curves for the superconducting point contacts in the frequency range 5-30 cm-1 are presented. The condition need for achieving high sensitivity of superconducting point contacts and superconducting bridges are determined.On présente les calculs, de la caractéristique V-I d'une jonction Josephson shuntée par une résistance, de son impédance en haute fréquence et de sa réponse à un petit signal externe. On donne les courbes expérimentales obtenues dans le domaine de longueurs d'onde de 5 à 30 cm et on précise les conditions optimales de fonctionnement pour les contacts à pointes et les microponts