Tunnelling characteristics of point contacts with high Tc material

Abstract

The I– V characteristics of point contacts formed by pressing two pieces of bulk material against each other are considered. One side of the contact consists of a ceramic superconductor. The other side can be either a ceramic superconductor, a normal metal or a classical superconductor. The I– V characteristics of the contacts formed with these different materials often show a remarkable similarity: the I– V characteristics can be very well described by the phenomenological equation IR 0 = V{1 + ( V/ V 0) α }, where the exponent α is of the order of one and V 0 of the order of 100 mV. The parameters V 0 and α determine the shape of the curve. The temperature dependence of the curves is dominated by the temperature dependence of R 0. No significant changes are observed at the critical temperature of the superconducting materials. In this paper we show that the observations can be explained by assuming that normal electron tunnelling takes place across a trapezoidal potential barrier.