On the superconducting phase boundary for a mesoscopic square loop

A self-consistent solution of the Ginzburg-Landau equations for a mesoscopic superconducting square loop has been obtained. It has been shown that the inhomogeneous distribution of the amplitude of the order parameter inside the loop leads to the appearance of certain areas where it is much more difficult to rotate the superconducting condensate and which therefore sustain much higher applied magnetic fields. The interplay between the square symmetry of the loop and the cylindrical symmetry of the magnetic field results in different oscillatory superconducting phase boundaries which correspond to various phase boundary definitions. The most ''realistic'' criterion to define the phase boundary magnetic field(H)-temperature(T) is formulated; it allows to obtain a good agreement between the calculated H(T) curve and the experimentally observed one. Copyright (C) 1996 Elsevier Science Ltd