Vector field controlled vortex lattice symmetry in LiFeAs

TL;DR

This study uses vector magnetic fields and scanning tunneling microscopy to explore how vortex lattice symmetry in LiFeAs varies with magnetic field orientation and strength, revealing its connection to superconducting pairing mechanisms.

Contribution

It provides the first detailed 3D field-dependent phase diagram of vortex lattice symmetry in LiFeAs, linking vortex behavior to superconducting gap and pairing symmetry.

Findings

Hexagonal vortex lattice in zero field-cooled conditions

Transition to four-fold symmetry with increasing c-axis field

Correlation between vortex lattice distortion and superconducting gap

Abstract

We utilize a combination of vector magnetic field and scanning tunneling microscopy to elucidate the 3D field-based electronic phase diagram of a correlated iron-based superconductor, LiFeAs. We observe, under a zero-field-cooled method, an ordered hexagonal vortex lattice ground-state in contrast to the disordered lattice observed under a field-cooled method. It transforms into a four-fold-symmetric state by increasing c-axis field and distorts elliptically upon tilting the field in-plane. The vortex lattice transformations correlate with the field dependent superconducting gap that characterizes the Cooper pairing strength. The anisotropy of the vortex lattice agrees with the field enhanced Bogoliubov quasiparticle scattering channel that is determined by the pairing symmetry with respect to its Fermi surface structure. Our systematic tuning of the vortex lattice symmetry and study of its correlation with Cooper pairing demonstrates the many-body interplay between the superconducting order parameter and emergent vortex matter.