Phase Dependent Thermopower in Andreev Interferometers

Abstract

We report measurements of the thermopower $S$ of mesoscopic Andreev interferometers, which are hybrid loops with one arm fabricated from a superconductor (Al), and one arm from a normal metal (Au). $S$ depends on the phase of electrons in the interferometer, oscillating as a function of magnetic flux with a period of one flux quantum ${\ensuremath{\Phi}}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}h/2e$. The magnitude of $S$ increases as the temperature $T$ is lowered, reaching a maximum at $T\ensuremath{\sim}0.14$ K, and decreases at lower temperatures. The symmetry of $S$ oscillations with respect to magnetic flux depends on the topology of the sample.