Competition between Josephson and electromagnetic interactions in single crystals

Abstract

We have studied the low magnetic field, high-temperature region of the H-T phase diagram of (Bi2212) single crystals by measuring magnetic field induced rf dissipation in the mixed state. Normally the rf power loss P(H) versus H in a superconductor increases with the increase in the field with a minimum at H = 0. However, in Bi2212 the rf loss initially decreases with increasing field, shows a minimum at a certain field and increases continuously beyond . We understand the unusual minimum at as resulting from a competition between (i) the increasing attractive electromagnetic interaction between the pancake vortices (that constitute the vortex line) in adjacent bilayers with the increasing field and (ii) the decreasing Josephson coupling between the CuO bilayers with the increase in the field. The line defines a new boundary in the H-T phase diagram at which the tilt modulus of the 2D vortex stack in Bi2212 is at a maximum. It is found to obey the behaviour with the exponent n = 3/2 reminiscent of the predicted behaviour of the melting line.