Josephson effect between superconductors in possibly different spin-pairing states

Pals, J.A.; Haeringen, W. van; Maaren, M.H. van

doi:10.1103/physrevb.15.2592

Cited by 91 publications

(35 citation statements)

References 21 publications

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“…For nonmagnetic barriers and in the absence of spin-orbit, there is no spin-flip scattering, thereforeT k = 0 and the Josephson current vanishes identically [21,23,24]. From Eqs.…”

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confidence: 99%

Phase-Sensitive Tests of the Pairing State Symmetry inSr2RuO4

Žutić

Mazin

2005

Phys. Rev. Lett.

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Exotic superconducting properties of Sr2RuO4 have provided strong support for an unconventional pairing symmetry. However, the extensive efforts over the past decade have not yet unambiguously resolved the controversy about the pairing symmetry in this material. While recent phase-sensitive experiments using flux modulation in Josephson junctions consisting of Sr2RuO4 and a conventional superconductor have been interpreted as conclusive evidence for a chiral spin-triplet pairing, we propose here an alternative interpretation. We show that an overlooked chiral spin-singlet pairing is also compatible with the observed phase shifts in Josephson junctions and propose further experiments which would distinguish it from its spin-triplet counterpart.Unambiguous determination of the pairing state symmetry is one of the key steps towards understanding the pairing mechanism in a continously growing class of unconventional superconductors [1]. Phase-sensitive experiments, capable of identifying angular dependence of the superconducting order parameter, have provided a crucial evidence for a dominant d-wave orbital symmetry in cuprate superconductors [2,3,4]. However, much less is known for other unconventional superconductors such as heavy fermions, charge transfer salts, and cobaltates. In particular, there is compelling evidence for an unconventional pairing in Sr 2 RuO 4 [5,6], with the strong possibility of spin-triplet superconductivity which would be a solid-state analog of superfluid He 3 [7]. In superconductors with inversion symmetry an order parameter (gap matrix) can be expressed as∆(k) = ∆ 0 (k)iσ y for spin singlet and∆(k) =σ · d(k)iσ y for spin-triplet pairing. Hereσ are the Pauli spin matrices and scalar (vector) ∆ 0 (d) has even (odd) parity in the wavevector k. Often the symmetry of both the orbital and the spin part of∆(k) remains to be identified and the lack of related understanding comes from the difficulty in performing phase-sensitive experiments.While numerous previous experiments probed the pairing symmetry of Sr 2 RuO 4 [6], in this context, recent phase-sensitive experiments [8] that provide angleresolved information are particularly important. The corresponding measurements were performed in a superconducting quantum interference device (SQUID) geometry, consisting of a pair of Au 0.5 In 0.5 /Sr 2 RuO 4 Josephson junctions. Since Au 0.5 In 0.5 is a conventional s-wave superconductor, the observed modulation of critical current in an applied magnetic field was interpreted as conclusive support for the phase shifts from an odd-parity spin-triplet pairing in Sr 2 RuO 4 [8,9].A similar SQUID geometry was initially proposed [10] to study possible p-wave pairing in heavy fermions and later also used for identifying d-wave pairing in cuprates [2]. The critical current I c is modulated in the applied magnetic field as [11]where Φ is the flux threading the SQUID, Φ 0 is the flux quantum, and δ 12 is the intrinsic phase shift of the order parameter between the two tunneling directions. For a conventional ...

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“…For nonmagnetic barriers and in the absence of spin-orbit, there is no spin-flip scattering, thereforeT k = 0 and the Josephson current vanishes identically [21,23,24]. From Eqs.…”

mentioning

confidence: 99%

Phase-Sensitive Tests of the Pairing State Symmetry inSr2RuO4

Žutić

Mazin

2005

Phys. Rev. Lett.

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“…There are other physical resources, which have not yet been employed in RQ designing. One of most interesting is the effect of disappearance of coherent effects between s-and p-wave pairing superconductors [26]. This effect is valid in absence of spin-orbital coupling and for ruthenates this coupling seems not to be strong.…”

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confidence: 99%

Triplet superconductors from the viewpoint of basic elements for quantum computers

Gulian

Wood

2003

IEEE Trans. Appl. Supercond.

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Abstract-We discuss possibilities of utilizing superconductors with Cooper condensates in triplet pairing states (where the spin of condensate pairs is S=1) for practical realization of quantum computers. Superconductors with triplet pairing condensates have features that are unique and cannot be found in the usual (singlet pairing, S=0) superconductors. The symmetry of the order parameter in some triplet superconductors (e.g., ruthenates) corresponds to doubly-degenerate chiral states. These states can serve as qubit base states for quantum computing.

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“…20) Due to the spin-orbit coupling in UPt 3 , the spin-triplet parings are actually the odd-parity parings, i.e. a triplet state is formed in the pseudospin, which is a superposition of the states with different spins.…”

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confidence: 99%

Josephson Current between Triplet and Singlet Superconductors

Hasegawa

1998

J. Phys. Soc. Jpn.

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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...

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Josephson effect between superconductors in possibly different spin-pairing states

Cited by 91 publications

References 21 publications

Phase-Sensitive Tests of the Pairing State Symmetry inSr2RuO4

Phase-Sensitive Tests of the Pairing State Symmetry inSr2RuO4

Triplet superconductors from the viewpoint of basic elements for quantum computers

Josephson Current between Triplet and Singlet Superconductors

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