Fermi surface and order parameter driven vortex lattice structure transitions in twin-free YBa2Cu3O7

TL;DR

This study uses small-angle neutron scattering to explore vortex lattice structures in detwinned YBa2Cu3O7, revealing field-driven phase transitions influenced by Fermi surface and order parameter anisotropies.

Contribution

It identifies and characterizes two first-order vortex lattice transitions in detwinned YBa2Cu3O7, linking them to Fermi surface effects and order parameter anisotropy.

Findings

Discovery of a new distorted hexagonal vortex lattice phase at intermediate fields.

Identification of a first-order transition at 2.0 T driven by Fermi surface effects.

Observation of a crossover at 6.7 T influenced by order parameter anisotropy.

Abstract

We report on small-angle neutron scattering studies of the intrinsic vortex lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8 T. Because of the suppressed pinning to twin-domain boundaries, a new distorted hexagonal VL structure phase is stabilized at intermediate fields. It is separated from a low-field hexagonal phase of different orientation and distortion by a first-order transition at 2.0(2) T that is probably driven by Fermi surface effects. We argue that another first-order transition at 6.7(2) T, into a rhombic structure with a distortion of opposite sign, marks a crossover from a regime where Fermi surface anisotropy is dominant, to one where the VL structure and distortion is controlled by the order-parameter anisotropy.