Response of a $d_{x^2-y^2}$ Superconductor to a Zeeman Magnetic Field

Abstract

We study the response of a two dimensional $d_{x^2-y^2}$ superconductor to a magnetic field that couples only to the spins of the electrons. In contrast to the s-wave case, the $d_{x^2-y^2}$ state is modified even at small magnetic fields, with the gap nodes widening into normal, spin polarized, pockets. We discuss the promising prospects for observing this in the cuprate superconductors in fields parallel to the Cu-O planes. We also discuss the phase diagram, inclusive of a finite momentum pairing state with a novel linkage between the momentum of the pairs and the nodes of the relative wave function.

An error in the calculation of the phase boundary separating the normal state and FFLO state corrected; Figure 2 modified. No change has been made to the part on weak field response. Final version to appear in PRB