Hexagonal and Square Flux Line Lattices in CeCoIn5

TL;DR

This study uses small-angle neutron scattering to image the flux line lattice in CeCoIn5, revealing a transition from hexagonal to square symmetry aligned with theoretical predictions for d-wave superconductors.

Contribution

First direct imaging of flux line lattice symmetry transition in CeCoIn5, confirming theoretical predictions for d-wave superconductors.

Findings

Hexagonal flux line lattice at low fields

First-order transition to square lattice at ~0.6 T

Square lattice aligned with gap node directions

Abstract

Using small-angle neutron scattering, we have imaged the magnetic flux line lattice (FLL) in the d-wave heavy-fermion superconductor CeCoIn5. At low fields we find a hexagonal FLL. Around 0.6 T this undergoes what is very likely a first-order transition to square symmetry, with the nearest neighbors oriented along the gap node directions. This orientation of the square FLL is consistent with theoretical predictions based on the d-wave order parameter symmetry.