Periodic oscillations of the critical temperature versus the applied magnetic flux in a four-terminal SQUID

Abstract

Small changes in the critical temperature, which are periodic in the applied magnetic flux, are observed in a four-terminal SQUID, i.e. a SQUID interrupted by a four-terminal Josephson junction. This novel effect is discussed for a conventional two-terminal SQUID, consisting of a weak constriction, by applying thermodynamics in the Ginzburg-Landau regime. Special attention is paid to the case of a SQUID ring with very small self-inductance in an applied magnetic flux of an odd amount of half magnetic flux quanta so that no circulating current is present. An extension is made to the case of the four-terminal SQUID to demonstrate that the theory for the two-terminal SQUID also applies to the experimentally used four-terminal case.