Magnetic field necessary to destroy superconductivity in Al-type Se and Te

Abstract

This paper reports the results of a study of the critical magnetic field required to restore electrical resistance in superconducting metastable Al-type Se and Te overlays vapor-quenched, respectively, on MgO, FeO, CoO, or NiO and CaO or MnO base films quench-condensed on glass substrates. The critical field was measured at various temperatures, from the superconducting transition temperature in zero field down to 0.1 K, for overlay thicknesses ranging from 100 Å up to values at which size effects disappear. The measurements were repeated after cyclic annealing at increasing temperatures up to a limiting temperature at which the overlay breaks owing to the transformation of the A1-type modification to the less dense ordinary A8-type structure.The critical field decreases steeply, with increasing thickness, down to a constant bulk-material value, increases nearly parabolically, with decreasing temperature, up to an extrapolable absolute-zero value, and decreases irreversibly with increasing annealing temperature. The superconducting-to-normal phase transition occurs through an intermediate state, which indicates that quench-deposited A1-type Se and Te are soft superconductors.