Variable superconducting quantum-interference device: Theory

H. J. Fink; V. Grünfeld; S. M. Roberts

doi:10.1103/PhysRevB.36.74

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Variable superconducting quantum-interference device: Theory

H. J. Fink, V. Grünfeld, S. M. Roberts

DOI 10.1103/PhysRevB.36.74 · Physical Review B

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Abstract

A dc superconducting quantum interference device (SQUID) consisting of a symmetric ring circuit with four Josephson junctions and two independent external currents I1 and I2, which enter the circuit at different points, has a phase boundary between the fully superconducting and the normal states that is different from that of a conventional SQUID. The control current I2 modifies the magnetic flux (φ) periodicity and the value of the maximum measuring current I1m(φ). For values of I2>Ic (critical current of Josephson junction) the fully resistive state exists over flux intervals centered around (n+(1/2)φ0, where n is an integer and φ0 is the fluxoid quantum. A superconducting circuit without Josephson junctions is suggested which should have a phase boundary similar to that found here. Minimization procedures which are usually employed in analyzing SQUID’s are discussed.