Vector field STM study of iron-based superconductor*

Magnetic field studies of iron-based superconductors have been largely limited to c-axis applied fields. Using a combination of a vector magnetic field and high resolution scanning tunneling microscopy/spectroscopy, we study the three dimensional field based phase diagram of vortex electronic matter in a correlated iron-based superconductor. We find that the lattice structure of the vortices is strongly correlated with the magnitude and direction of the magnetic field in an anisotropic manner. Probing the quasiparticle excitations and interferences reveals an unusual magnetic pair-breaking effect with distinct scattering vectors. These results will help us understand the interplay between Cooper pairing and emergent three dimensional vortex matter in iron-based superconductors.