Anisotropy of in-plane magnetization due to nodal gap structure in the vortex state

TL;DR

This paper investigates how the anisotropy in in-plane magnetization relates to the nodal gap structure in vortex states of type II superconductors, revealing a four-fold oscillation pattern with sign changes influenced by field and temperature.

Contribution

It provides an analytic framework linking magnetization anisotropy to nodal gap structures, enabling direct experimental identification of gap symmetry in superconductors.

Findings

Four-fold oscillation in magnetization with sign change at intermediate fields.

High-field oscillation driven by upper critical field anisotropy.

Low-field behavior explained by thermally activated quasiparticles near nodes.

Abstract

We examine the interplay between anisotropy of the in-plane magnetization and the nodal gap structure on the basis of the approximate analytic solution in the quasiclassical formalism. We show that a four-fold 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.