Josephson Current between Triplet and Singlet Superconductors

Abstract

The Josephson effect between triplet and singlet superconductors is studied. Josephson current can flow between triplet and singlet superconductors due to the spin-orbit coupling in the spintriplet superconductor but it is finite only when triplet superconductor has Lz = −Sz = ±1, where Lz and Sz are the perpendicular components of orbital angular momentum and spin angular momentum of the triplet Cooper pairs, respectively. The recently observed temperature and orientational dependence of the critical current through a Josephson junction between UPt3 and Nb is investigated by considering a non-unitary triplet state.KEYWORDS: triplet superconductor, odd-parity, spin-orbit coupling Josephson junction Superconductivity in UPt 3 attracts a lot of interests. The existence of two different superconducting phases (A and B phases) as well as the third phase in the magnetic field (C phase) shows that the superconductivity in this system is not a conventional s-wave spin-singlet superconductivity. The possibility of the triplet superconductivity has been discussed.1, 2, 3, 4) The anisotropy of H c2 5) is discussed as an evidence for the triplet superconductivity with the d vector parallel to the c-axis. 2)Experimental results of the Knight shift observed by the NMR 6,7,8) and µSR 9) show the evidence for the triplet superconductivity in UPt 3 .10) The Knight shift is observed to be independent of temperature in the superconducting phase for H > 5 kOe.6, 7, 8) It decreases below T + c (A and B phases) for H < 5 kOe when H b and below T − c (B phase) for H < 2.3 kOe when H ĉ.8) The spin susceptibility for the spin-singlet superconductivity decreases as temperature becomes low, while that for the spin-triplet superconductivity is independent of temperature if the magnetic field is perpendicular to the d vector. Therefore, the magnetic-field and temperature dependences of the Knight sift of UPt 3 can be understood by the spin triplet states. The A and B phases are identified with respectively. 8, 11, 10) Since the Josephson effect is controlled by both the amplitude and the phase of the order parameters, it is a powerful tool to identify the symmetry of the order parameters. Recently, Sumiyama et al.12) have observed the Josephson critical current between a single crystal UPt 3 and an s-wave superconductor Nb. They also observed the Shapiro steps of thehω/(2e). If the Josephson current is caused by the higher-order tunneling or the proximity induced tunneling, the steps ofhω/(2ne) with n ≥ 2 should be observed. 13,14) Thus it is concluded that the Josephson current between UPt 3 and Nb is caused by the ordinary pair tunneling of the Cooper pairs. They found that the critical current is very small in the A phase and it increases steeply as temperature becomes lower than T The order parameters near the interface may be different from those in the bulk. Recently, it has been shown that the localized zero energy state exists at the interface when the order parameter change sign through the reflection.15) The zero energy stat...

Phase Dependent Energy Levels of Bound States and D.C. Josephson Current in Unconventional Superconductor / Ferromagnetic Insulator / Unconventional Superconductor Junctions

“…However, the finite amplitude of the SO interaction possibly exists at the boundary of p-wave superconductor, which may have large influences on the Josephson effect between triplet superconductors and singlet ones. 23,24,67,[84][85][86] In previous papers, the Hamilotonian in the tunneling limit in the presence of the SO coupling is given by, 23,86) recovers even without the exchange interaction in the insulator (Z m0 = 0).…”

Josephson current ins-wave-superconductor/Sr2RuO4junctions

“…[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] This state breaks time reversal symmetry with an angular momentum along the c-axis and has inplane equal spin pairing. 38 So far the transport properties in junctions consisting of SRO and s-wave superconductors or normal metals have been studied in both theories [53][54][55][56][57][58] and experiments. [59][60][61][62] The effect of spin-orbit coupling, where it had been taken into account, was introduced in the form of effective matrix elements only without the care of a detailed microscopic model for their origin.…”

Josephson effect between conventional and Rashba superconductors

“…The influences of such bound states have been neglected here for the qualitative discussions as in Refs. [11,12,14,15]. A more detailed analysis taking these aspects into account is left for future studies.…”

“…Note that from Eq. (14) it follows that w is real, and the factor Im{λ · w * Ψ s ∆ * I,II } in Eq. (12) leads toλ · w|Ψ s ||∆ I,II | sin φ ph .…”

“…The Josephson effect between a conventional (s-wave spin-singlet) and an unconventional superconductor provides a possible way to probe the spin structure of the unconventional Cooper pairing state [11][12][13][14][15]. For the noncentrosymmetric superconductor CePt 3 Si, an experiment in this direction was recently performed by Sumiyama et al [16].…”