Finite momentum superconductivity in superconducting hybrids: Orbital mechanism

Normally, in superconductors, as in conductors, in a state with zero current I the momentum of superconducting electrons (h) over barq = 0. Here we demonstrate theoretically and present experimental evidence that in a superconducting/normal metal (SN) hybrid strip placed in an in-plane magnetic field Bin a finite momentum state ((h) over barq = 0) is realized when I = 0. This state is characterized by current-momentum dependence I (q) not equal -I (-q), nonreciprocal kinetic inductance L-k (I) not equal L-k (-I), and different values of depairing currents I-dep(+/-) flowing along the SN strip in opposite directions. The properties found have orbital nature and originate from the density gradient of superconducting electrons del n across the thickness of the SN strip and field-induced Meissner currents. We argue that this type of finite momentum state should be a rather general phenomenon in superconducting structures with artificial or intrinsic inhomogeneities.