Vector field controlled vortex lattice symmetry in LiFeAs using scanning tunneling microscopy

We utilize a combination of vector magnetic field and scanning tunneling microscopy to elucidate the three-dimensional 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 to a fourfold-symmetric state by increasing the 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 in 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.