Thermoelectric and thermophase effects in Josephson junctions

Abstract

We study the thermoelectric properties of a superconductor-insulator-superconductor Josephson junction. The total electrical current across the junction is composed of three parts: a normal current, a Josephson current, and an interference current. We show that only the normal part contributes to a thermocurrent (i.e., an electrical current that flows in response to a temperature drop). The fact that the interference current has no thermoelectric properties provides insight into the physical nature of this term. We distinguish between two mechanisms for the thermocurrent: one is the normal thermoelectric tunneling current; the other is a transport phenomenon, which ensues from a nonequilibrium (charge-imbalance) state in the bulk superconductors comprising the junction. The latter effect gives rise to a phase-dependent thermocurrent. Finally, we consider an open-circuit Josephson junction biased by a temperature drop. The possible steady states of the system are studied using the resistively shunted junction model. In particular, we consider the zero-voltage state which corresponds to canceling of the quasiparticle and condensate currents. We call this a thermophase effect. Experimental setups are suggested in order to detect this effect.

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