Origin of spontaneous broken mirror symmetry of vortex lattices in Nb

TL;DR

This study combines microscopic theory and first principles calculations to explain the spontaneous broken mirror symmetry in vortex lattices of cubic Nb, revealing how Fermi surface properties influence lattice morphologies.

Contribution

It introduces a minimal Fermi surface model that explains the stability of scalene triangle vortex lattices due to broken mirror symmetry in Nb.

Findings

FLL transformations along Hc2 are explained without adjustable parameters.

The stability of scalene triangle lattices is linked to Fermi surface asymmetry.

Various vortex lattice geometries are predicted as temperature increases.

Abstract

Combining the microscopic Eilenberger theory with the first principles band calculation, we investigate the stable flux line lattice (FLL) for a field applied to the four-fold axis; $H\parallel [001]$ in cubic Nb. The observed FLL transformation along $H_{c2}$ is almost perfectly explained without adjustable parameter, including the tilted square, scalene triangle with broken mirror symmetry, and isosceles triangle lattices upon increasing $T$. We construct a minimum Fermi surface model to understand those morphologies, in particular the stability of the scalene triangle lattice attributed to the lack of the mirror symmetry about the Fermi velocity maximum direction in k-space.