Magnetic field dependence of the quantum tunneling of normal-superconductor interfaces in a type-I Pb superconductor

Abstract

We report experimental evidence of the effect of an applied magnetic field on the non-thermal magnetic relaxation in a disk-shaped type-I lead superconductor. The time evolution of the irreversible magnetization proves to be logarithmic for a wide range of temperatures and magnetic field values along the descending branch of the hysteresis cycle. When the intensity of the magnetic field increases, the crossover temperature separating the thermal and non-thermal regimes of magnetic relaxation is found to decrease, whereas the rate at which such relaxation occurs is observed to increase. These results are discussed in the framework of a recent model for quantum tunneling of normal-superconductor interfaces through the distribution of pinning energy barriers generated by structural defects in the sample, considering that the strength of the barriers decreases with the magnetic field. A phase diagram describing the dynamics of interfaces during flux expulsion in the intermediate state as a function of temperature and magnetic field is constructed.

The role of temperature in the magnetic irreversibility of type-I Pb superconductors

“…In accordance with this picture, magnetic relaxation has been proved to occur in disks after starting at any point along m des (h) when h < h * [30]. The average size of the pinning barriers at zero magnetic field, U 0 ≡ U(0), was recently estimated to be roughly 100 K from magnetic relaxation experiments in a system like sample A [20].…”

“…Therefore, magnetic experiments involving other type-I superconductors are encouraged to be performed as they should help to shed light on this issue. Finally, the discussion of the magnetic field dependence of the low-temperature relaxation rate of a disk in terms of the QTI model, assuming that the pinning energy barriers decrease with the magnetic field as suggested here, has been the subject of a recent publication [30].…”