Anomalous Josephson current, incipient time-reversal symmetry breaking, and Majorana bound states in interacting multilevel dots

Brunetti, Aldo; Zazunov, Alex; Kundu, Arijit; Egger, Reinhold

doi:10.1103/physrevb.88.144515

Cited by 108 publications

(82 citation statements)

References 68 publications

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“…This effect is referred to as the anomalous Josephson effect (AJE) and takes place only in systems with a broken time-reversal symmetry. The AJE has been predicted in junctions which combine conventional superconductors with magnetism and spinorbital interaction [15][16][17][18][19][20][21][22][23], between unconventional superconductors [24], and between topologically nontrivial superconducting leads [25]. In the presence of magnetic flux piercing the normal interlayer superconducting proximity currents are generated, which naturally leads to a phase shift of the CPR [26,27].…”

Section: Introductionmentioning

confidence: 99%

Anomalous current in diffusive ferromagnetic Josephson junctions

2017

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We demonstrate that in diffusive superconductor/ferromagnet/superconductor (S/F/S) junctions a finite, anomalous Josephson current can flow even at zero phase difference between the S electrodes. The conditions for the observation of this effect are noncoplanar magnetization distribution and a broken magnetization inversion symmetry of the superconducting current. The latter symmetry is intrinsic for the widely used quasiclassical approximation and prevented previous works based on this approximation from obtaining the Josephson anomalous current. We show that this symmetry can be removed by introducing spin-dependent boundary conditions for the quasiclassical equations at the superconducting/ferromagnet interfaces in diffusive systems. Using this recipe, we consider generic multilayer magnetic systems and determine the ideal experimental conditions in order to maximize the anomalous current.

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Section: Introductionmentioning

confidence: 99%

Anomalous current in diffusive ferromagnetic Josephson junctions

2017

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“…This is the so called ϕ 0 -junction, and its interpretation in terms of the inverse magneto-electric effect was reported in 46 . It was actively studied recently in half-metal junctions, noncoplanar ferromagnetic junctions, ferromagnetic Josephson junctions with spin orbit interaction or TI surface states [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] .…”

Section: Introductionmentioning

confidence: 99%

Quasiclassical theory of magnetoelectric effects in superconducting heterostructures in the presence of spin-orbit coupling

Bobkova

Bobkov

2017

Phys. Rev. B

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The quasiclassical theory in terms of equations for the Green's functions (Eilenberger equations) is generalized in order to allow for quantitative description of the magneto-electric effects and proximity-induced triplet correlations in the presence of spin-orbit coupling in hybrid superconducting systems. The formalism is valid under the condition that the spin-orbit coupling is weak with respect to the Fermi energy, but exceeds the superconducting energy scale considerably. On the basis of the derived formalism it is shown that the triplet correlations in the spin-orbit coupled normal metal can be induced by proximity to a singlet superconductor without any exchange or external magnetic field. They contain an odd-frequency even-momentum component, which is stable against disorder. The value of the proximity-induced triplet correlations is of the order of ∆so/εF , that is absent in the framework of the standard quasiclassical approximation, but can be described by our theory. The spin polarization, induced by the Josephson current flowing through the superconductor/Rashba metal/superconductor junction, is also calculated.

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“…Interestingly, the ingredients for observing a ϕ 0 JJ in this type of system largely overlap with those required to generate MBSs. In this work, we focus on two models for ϕ 0 JJs based on QDs which, compared to previous studies [35][36][37], are in the singlet-triplet anticrossing regime. In the first model, two s-wave SCs are tunnel coupled via a two-orbital QD with SOI and subject to a Zeeman field, see Fig.…”

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confidence: 99%

Detecting topological superconductivity with φ0 Josephson junctions

2017

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The interplay of superconductivity, magnetic fields, and spin-orbit interaction lies at the heart of topological superconductivity. Remarkably, the recent experimental discovery of ϕ0 Josephson junctions by Szombati et al. [1], characterized by a finite phase offset in the supercurrent, require the same ingredients as topological superconductors, which suggests a profound connection between these two distinct phenomena. Here, we theoretically show that a quantum dot ϕ0 Josephson junction can serve as a new qualitative indicator for topological superconductivity: Microscopically, we find that the phase shift in a junction of s−wave superconductors is due to the spin-orbit induced mixing of singly occupied states on the qantum dot, while for a topological superconductor junction it is due to singlet-triplet mixing. Because of this important difference, when the spin-orbit vector of the quantum dot and the external Zeeman field are orthogonal, the s-wave superconductors form a π Josephson junction while the topological superconductors have a finite offset ϕ0 by which topological superconductivity can be distinguished from conventional superconductivity. Our prediction can be immediately tested in nanowire systems currently used for Majorana fermion experiments and thus offers a new and realistic approach for detecting topological bound states. Non-abelian anyons are the building blocks of topological quantum computers [2]. The simplest realization of a non-abelian anyon are Majorana bound states (MBSs) in topological superconductors (TSs) [3]. It has been proposed that such a TS can be induced by an s-wave superconductor (SC) in systems of nanowires with spinorbit interaction (SOI) subject to a Zeeman field [4][5][6][7], in chains of magnetic atoms [8][9][10][11] and in topological insulators [12][13][14][15][16][17]. However, providing experimental evidence for the existence of this new phase of matter has remained a major challenge.Here we present a new qualitative indicator of MBS based on ϕ 0 Josephson junctions (ϕ 0 JJs). In ϕ 0 JJs the Josephson current is offset by a finite phase, ϕ 0 , so that a finite supercurrent flows even when the phase difference between the superconducting leads and the magnetic flux enclosed by the Josephson junction (JJ) vanishes. Such ϕ 0 JJs have been discussed in systems based on unconventional superconductors [18][19][20][21][22] [32,33]. Recently, the connection between ϕ 0 JJs based on nanowires and TSs has also been discussed [34]. Most relevant for the present work, the emergence of a ϕ 0 JJ was theoretically predicted [35][36][37] in a system of a quantum dot (QD) with SOI subject to a Zeeman field when coupled to s-wave superconducting leads and observed in recent experiments [1]. Interestingly, the ingredients for observing a ϕ 0 JJ in this type of system largely overlap with those required to generate MBSs. In this work, we focus on two models for ϕ 0 JJs based on QDs which, compared to previous studies [35][36][37], are in the singlet-triplet anticrossing regime. In the...

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Anomalous Josephson current, incipient time-reversal symmetry breaking, and Majorana bound states in interacting multilevel dots

Cited by 108 publications

References 68 publications

Anomalous current in diffusive ferromagnetic Josephson junctions

Anomalous current in diffusive ferromagnetic Josephson junctions

Quasiclassical theory of magnetoelectric effects in superconducting heterostructures in the presence of spin-orbit coupling

Detecting topological superconductivity with φ0 Josephson junctions

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