Vortex lattice transition in D-wave superconductors

TL;DR

This paper investigates how higher order derivatives in the extended Ginzburg Landau theory cause vortex core distortion and a transition to a square vortex lattice in D-wave superconductors, with a focus on the transition's first-order nature.

Contribution

It introduces the effect of fourth order derivative terms on vortex structures and lattice transitions in D-wave superconductors, revealing a first-order transition to a tilted square lattice.

Findings

Vortex core structure is distorted with fourfold symmetry.

A transition to a tilted square vortex lattice occurs.

Magnetization diverges at the transition, indicating first-order behavior.

Abstract

Making use of the extended Ginzburg Landau theory, which includes the fourth order derivative term, we study the vortex state in a magnetic field parallel to the $ c$ axis. The vortex core structure is distorted due to this higher order term, which reveals t he fourfold symmetry. Futher, this distortion gives rise to the core interaction energy, which favo rs a square lattice tilted by $45^\circ$ from the $a$ axis. The critical field of this transition is determined. The magnetization diverges at the transition. This suggests the transition is of the fi rst order.