Surface pair-density-wave state and generalisation of Fulde-Ferrell-Larkin-Ovchinnikov state to chiral and nematic superconductors*

The paramagnetic interaction between the applied magnetic field and the spin of the electrons in a superconductor may lead to the formation of Cooper pairs with non-zero momentum. This results in inhomogeneous superconducting states, breaking translational symmetry, which characterizes the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We find that the transition from the FFLO to normal state is not direct. As temperature or applied magnetic field is increased, superconductivity vanishes first in the bulk while the pair-density-waves (PDW) exist on the boundaries. The surface PDW state can exist for significantly larger field and temperature than the FFLO state. I will also discuss generalisation of FFLO states to systems with unconventional pairing. One of the found states is a nematic superconductor where the nematicity vector breaks rotational and translational symmetries due to spontaneous spatial modulation. Another state is a chiral superconductor with spontaneously broken time reversal and translational symmetries, resulting in spatially alternating chirality.

References:
arXiv:1811.09590
arXiv:1811.10594