Paramagnetic Intrinsic Meissner Effect in Layered Superconductors

Abstract

Free energy of a layered superconductor with $\xi_{\perp} < d$ is calculated in a parallel magnetic field by means of the Gor'kov equations, where $\xi_{\perp}$ is a coherence length perpendicular to the layers and $d$ is an inter-layer distance. The free energy is shown to differ from that in the textbook Lawrence-Doniach model at high fields, where the Meissner currents are found to create an unexpected positive magnetic moment due to shrinking of the Cooper pairs "sizes" by a magnetic field. This paramagnetic intrinsic Meissner effect in a bulk is suggested to detect by measuring in-plane torque, the upper critical field, and magnetization in layered organic and high-T$_c$ superconductors as well as in superconducting superlattices.