Surface pair-density-wave superconductivity

Abstract

Fulde, Ferrell and Larkin, Ovchinnikov predicted inhomogeneous superconducting ground states, spontaneously breaking translation symmetries (FFLO states). Those states, under certain conditions, have lower energy than normal or homogeneous superconducting states, for example in the presence of strong Zeeman splitting of the Fermi surfaces. In this paper, we demonstrate that in a finite system, the transition from the FFLO to normal state as a function of temperature or increased Fermi surface splitting is not a direct one. Instead the system has additional phase where pair-density-wave superconductivity exists only on the surface of the system but the bulk of material is normal. The surface pair-density-wave superconductivity is very robust and and can exist for much larger fields and temperatures than FFLO state.