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

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.

Main text 5 pages, 3 figures, total 9 pages supplementary material included