# Generic First Order Orientation Transition of Vortex Lattices in Type II Superconductors

## TL;DR

This paper explains the first order transition of vortex lattices in four-fold symmetric type II superconductors using a microscopic theory, revealing it as an intrinsic phase transition caused by anisotropies and underlying symmetry frustrations.

## Contribution

It provides a microscopic explanation for the universal first order vortex lattice transition in superconductors with four-fold symmetry, linking it to anisotropies and symmetry frustrations.

## Key findings

- Transition is intrinsic and universal in such superconductors.
- Transition is driven by gap or Fermi velocity anisotropies.
- Electronic states around vortices support the transition mechanism.

## Abstract

First order transition of vortex lattices (VL) observed in various superconductors with four-fold symmetry is explained microscopically by quasi-classical Eilenberger theory combined with nonlocal London theory. This transition is intrinsic in the generic successive VL phase transition due to either gap or Fermi velocity anisotropies. This is also suggested by the electronic states around vortices. Ultimate origin of this phenomenon is attributed to some what hidden frustrations of a spontaneous symmetry broken hexagonal VL on the underlying four-fold crystalline symmetry.