The Symmetry of Phase-Coherent Thermopower Oscillations in Andreev Interferometers

We study the thermopower of diffusive Andreev interferometers, which are hybrid loops with one normal-metal arm and one superconducting arm. The thermopower oscillates as a function of the magnetic flux through the loop with a fundamental period corresponding to one flux quantum Φ0 = h/2e. Unlike the electrical resistance oscillations and the thermal resistance oscillations, which are always symmetric with respect to the magnetic field, the symmetry of the thermopower oscillations can be either symmetric or antisymmetric depending on the geometry of the sample. We also observe that the symmetry of the thermopower oscillations is related to the distribution of the supercurrent between the normal-metal/superconductor interfaces. We compare our experimental results with recent theoretical work.