Coupling of supercurrent and quasiparticle excitations in superconductor nanostructures

We report on the experimental observation of coupling between nonequilibrium modes of the quasiparticle excitations in thin superconducting films in the presence of supercurrent and high parallel magnetic fields. The coupling is due to a difference in the number of available quasiparticle states, depending on their relative propagation direction to the supercurrent. Recently the occurrence of a spinenergy (spin-antisymmetric charge imbalance) current in the presence
of energy imbalance was predicted [1]. Here the resulting spin-energy imbalance for a spatial gradient in the energy imbalance was probed in nonlocal conductance measurements with spectral resolution. The measurements show excellent agreement with numerical models and provide proof of the coupling of energy and spin-energy modes.