Journal of Applied Physics

Characteristics of superconducting quantum interference devices using multi-barrier superconducting junctions

Akiyoshi Nakayama, Takuma Sugio, Koji Manabe, Yoichi Okabe

Published Jun 1, 2001• 4 citations

Abstract

We have calculated the dc Josephson current through multi-barrier superconducting junctions (MBSJs). The current-phase relationship of the MBSJs has been obtained numerically from the probability amplitude of the process in which an electron-like quasiparticle is reflected as a hole-like quasiparticle (Andreev reflection) in the junctions. Moreover, using the obtained current-phase relationship of MBSJs, the characteristics of superconducting quantum interference devices containing MBSJs have also been analyzed.

DOI: 10.1063/1.1359461

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Journal of Applied Physics

Characteristics of superconducting quantum interference devices using multi-barrier superconducting junctions

Akiyoshi Nakayama, Takuma Sugio, Koji Manabe, Yoichi Okabe

Published Jun 1, 2001• 4 citations

Publisher

Abstract

DOI: 10.1063/1.1359461

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hc/4e

, which is the fingerprint of a transient intermediate state involving two entangled Cooper pairs. The quartet SQUID provides two pieces of information: an amplitude that measures a total ``quartet critical current,'' and a phase lapse coming from the superposition of the following two current components: the quartet supercurrent which is odd in the quartet phase, and the phase-sensitive multiple Andreev reflection (phase MAR) quasiparticle current, which is even in the quartet phase. This makes a TTJ a generically ``$\ensuremath{\theta}$ junction.'' Evidence for phase MARs plays against conservative scenarios involving synchronization of AC Josephson currents, based on ``adiabatic'' phase dynamics and resistively shunted junction--like models.

A dc superconducting quantum interference device (SQUID) consisting of a symmetric ring circuit with four Josephson junctions and two independent external currents

{I}_{1}

and

{I}_{2}

, 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

{I}_{2}

modifies the magnetic flux (\ensuremath{\varphi}) periodicity and the value of the maximum measuring current

{I}_{1m}

(\ensuremath{\varphi}). For values of

{I}_{2}

{I}_{c}

(critical current of Josephson junction) the fully resistive state exists over flux intervals centered around (n+(1/2)${\ensuremath{\varphi}}_{0}$, where n is an integer and ${\ensuremath{\varphi}}_{0}$ 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.