Shapiro steps as a direct probe of ±s-wave symmetry in multigap superconducting Josephson junctions

Yukihiro Ota; Masahiko Machida; Tomio Koyama

doi:10.1103/PhysRevB.82.140509

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Shapiro steps as a direct probe of ±s-wave symmetry in multigap superconducting Josephson junctions

Yukihiro Ota, Masahiko Machida, Tomio Koyama

DOI 10.1103/PhysRevB.82.140509 · Physical Review B

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Abstract

We theoretically study the Shapiro steps in a hetero-Josephson junction made of a single-gap superconductor and a two-gap one. We find that an anomalous dc Josephson current is induced by tuning the frequency of an applied microwave to the Josephson-Leggett mode frequency, which creates an extra step structure in the I−V characteristics besides the conventional Shapiro steps. The step heights at the resonance voltages exhibit an alternate structure of a large and small value reflecting the gap symmetry of the two-gap superconductor. In the ±s-wave case in which the two gaps have opposite signs in the two-gap superconductor the steps with odd index are enhanced, whereas in the s-wave case the ones with even index have larger values. The existence of the fractional Shapiro steps is also predicted.