DISSIPATION IN A ONE-DIMENSIONAL SUPERCONDUCTOR - EVIDENCE FOR MACROSCOPIC QUANTUM TUNNELING

The results of a study of the superconducting transition in very-small-diameter In wires are presented. Several different types of measurements have been performed. First, we have studied the resistive transition in the limit of low applied currents, i.e., IIc, where Ic is the critical current. Second, the transition to the dissipative state as a function of I has been examined. The results are discussed initially in terms of the thermal-activation model, according to which the dissipation is due to thermally activated motion of the Ginzburg-Landau order parameter over the free-energy barrier which separates metastable states. For certain ranges of sample size, temperature, and current, the thermal-activation theory is consistent with our results. However, for a wide range of these parameters we find that this theory fails, as the observed transition rates are much larger, and have a qualitatively different temperature dependence, than those predicted by the thermal-activation model. We suggest that in addition to thermal activation, quantum-mechanical tunneling of the order parameter through the free-energy barrier may also take place. We show that our results are consistent with this picture. © 1990 The American Physical Society.