Finite momentum superconductivity in superconducting hybrids: Orbital mechanism

Abstract

Normally in superconductors, as in conductors, in the state with zero current $I$ the momentum of superconducting electrons $\hbar q =0$. Here we demonstrate theoretically and present experimental evidences that in superconducting/normal metal (SN) hybrid strip placed in in-plane magnetic field $B_{in}$ finite momentum state ($\hbar q \neq 0$) is realized when $I=0$. This state is characterized by current-momentum dependence $I(q)\neq -I(-q)$, nonreciprocal kinetic inductance $L_k(I) \neq L_k(-I)$ and different values of depairing currents $I_{dep}^{\pm}$ flowing along the SN strip in opposite directions. Found properties have {\it orbital} nature and are originated from gradient of density of superconducting electrons $\nabla n$ across the thickness of SN strip and field induced Meissner currents. We argue that this type of finite momentum state should be rather general phenomena in superconducting structures with artificial or intrinsic inhomogeneities.