Paramagnetic intrinsic Meissner effect in layered superconductors

Free energy of a layered superconductor with ξ_⊥<d is calculated in a parallel magnetic field by means of the Gor’kov equations, where ξ_⊥ is a coherence length perpendicular to the layers and d is an interlayer 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 pair “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.