Magnetic-field-induced id_xy order in a d_x²−y² superconductor

Abstract

The interaction between planar quasiparticles in a d_x²−y² superconductor and quantized vortices associated with a magnetic field perpendicular to the plane is shown to induce a pair potential with d_xy symmetry, out of phase with the d_x²−y² order. A microscopic calculation of a process involving quasiparticle scattering by the supercurrent around a vortex and Andreev reflection from its core is presented. Other processes that also lead to an id_xy pair potential are discussed. It is argued that such a fully gapped state may be the high-field low-temperature phase observed by Krishana and Ong et al. in magnetothermal conductivity measurements of superconducting single-crystal Bi-2212.