Anisotropy of In-Plane Magnetization Due to Nodal Gap Structure in Vortex State

TLDR: In this paper, the interplay between the anisotropy of the in-plane magnetization and the nodal gap structure on the basis of the approximate analytic solution in quasi-classical formalism was examined.

Abstract: We examine the interplay between the anisotropy of the in-plane magnetization and the nodal gap structure on the basis of the approximate analytic solution in quasi-classical formalism. We show that a fourfold oscillation appears in the magnetization, and its amplitude changes sign at an intermediate field. The high-field oscillation originates from the anisotropy of the upper critical field, while the low-field behavior can be understood by the thermally activated quasiparticles near nodes depending on the applied field angles. The temperature dependence of the magnetization also shows a similar sign change. The anisotropy of the magnetization offers a possible measurement to identify the gap structure directly for a wide class of type II superconductors.