Evidence for a square-square vortex lattice transition in a high-$T_\textrm{c}$ cuprate superconductor

TL;DR

This study reports the discovery of a square-square vortex lattice transition in a high-$T_c$ cuprate superconductor, observed via sound measurements in high magnetic fields, confirming a predicted 45-degree rotation near a van Hove singularity.

Contribution

The paper provides experimental evidence for a vortex lattice transition in LSCO and offers a theoretical explanation based on Eilenberger theory, supporting long-standing predictions.

Findings

Identification of a new vortex lattice transition at high magnetic fields

Confirmation of a 45-degree rotation of the square vortex lattice

Theoretical support for the transition near a van Hove singularity

Abstract

Using sound velocity and attenuation measurements in high magnetic fields, we identify a new transition in the vortex lattice state of La$_{2-x}$Sr$_{x}$CuO$_4$ (LSCO). The transition, observed in magnetic fields exceeding 35 T and temperatures far below zero field $T_c$, is detected in the compression modulus of the vortex lattice, at a doping level $x=p=0.17$. Our theoretical analysis based on Eilenberger theory of vortex lattice shows that the transition corresponds to the long-sought 45 degrees rotation of the square vortex lattice, predicted to occur in $d$-wave superconductors near a van Hove singularity.