General framework for transport in spin-orbit-coupled superconducting heterostructures: Nonuniform spin-orbit coupling and spin-orbit-active interfaces

Sun, Kuei; Shah, Nayana

doi:10.1103/physrevb.91.144508

Cited by 29 publications

(22 citation statements)

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“…The calculated conductance features of SOC [42][43][44][45][46] can be distinguished from k-independent spin-flip scattering by magnetic moments: For Z ¼ 0 SOC always reduces the conductance and the subgap conductance vanishes for P ¼ 1. In contrast, k-independent spin-flip scattering [47] can increase the conductance and the subgap conductance is in general finite for P ¼ 1.…”

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confidence: 97%

Magnetoanisotropic Andreev Reflection in Ferromagnet-Superconductor Junctions

et al. 2015

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Andreev reflection spectroscopy of ferromagnet-superconductor (FS) junctions is an important probe of spin polarization. We theoretically investigate spin-polarized transport in FS junctions in the presence of Rashba and Dresselhaus interfacial spin-orbit fields and show that Andreev reflection can be controlled by changing the magnetization orientation. We predict a giant in-and out-of-plane magnetoanisotropy of the junction conductance. If the ferromagnet is highly spin polarized-in the half-metal limit-the magnetoanisotropic Andreev reflection depends universally on the spin-orbit fields only. Our results show that Andreev reflection spectroscopy can be used for sensitive probing of interfacial spin-orbit fields in a FS junction. DOI: 10.1103/PhysRevLett.115.116601 PACS numbers: 72.25.-b, 74.25.F-, 75.47.-m, 85.75.-d Spin-orbit coupling (SOC) is a key interaction in spintronics [1][2][3], allowing an electrical control of magnetization and, vice versa, a magnetic control of electrical current. In systems lacking space inversion symmetry-be it bulk, hybrid structures, junctions-SOC induces spinorbit fields [1,2] as an emergent phenomenon. We are in particular concerned here with interfacial spin-orbit fields which are believed to be behind a wealth of new phenomena, not existent or fragile in the bulk, such as the tunneling anisotropic magnetoresistance (TAMR) [4][5][6][7], interfacial spin-orbit torques [8], or Skyrmions [9].Interfacial spin-orbit fields are also important in semiconductor-superconductor [10-13] and ferromagnetsuperconductor (FS) junctions [14] for creating Majorana quasiparticle states. It is the latter junctions that we focus on. We investigate the interplay of magnetism and spin-orbit fields. We show that this interplay leads to marked anisotropies in the junction conductance with respect to the orientation of magnetization. The most robust is the outof-plane anisotropy (plane being the interface), which arises from the omnipresent Rashba field [15]. A more subtle is the in-plane anisotropy, which arises from the interference between the Rashba and Dresselhaus [16] fields, induced by a twofold anisotropy of the C 2v type. A zinc-blende semiconductor (say, GaAs or InAs) as a barrier in an FS junction would create such an anisotropy, generating spin-orbit fields C 2v "butterfly" patterns, as shown by first-principles calculations [17]. Remarkably, the resulting magnetoconductance anisotropy-we term it magnetoanisotropic Andreev reflection (MAAR)-is giant in comparison to TAMR, its normal-state counterpart, reaching a universal behavior in the half-metallic case. This is because Andreev reflection (AR) (which has no counterpart in the normal-state TAMR) is strongly influenced by interfacial spin-orbit fields.We specifically examine the influence of SOC and crystalline anisotropy on the process of AR in which the reflected particle carries the information about both the phase of the incident particle and the macroscopic phase of the superconductor to which a Cooper pair is being transferre...

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confidence: 97%

Magnetoanisotropic Andreev Reflection in Ferromagnet-Superconductor Junctions

et al. 2015

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“…An interesting expansion of the present work would be to explore how magnetic interfaces232425 and spin-orbit coupling would influence the proximity-gap phase diagram and topological properties of multiterminal Josephson junctions, as recent works have demonstrated that in particular the latter of these can induce several novel effects in both diffusive and ballistic superconducting hybrids13262728293031323334.…”

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confidence: 99%

Analytically determined topological phase diagram of the proximity-induced gap in diffusive n-terminal Josephson junctions

Amundsen

Ouassou

Linder

2017

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Multiterminal Josephson junctions have recently been proposed as a route to artificially mimic topological matter with the distinct advantage that its properties can be controlled via the superconducting phase difference, giving rise to Weyl points in 4-terminal geometries. A key goal is to accurately determine when the system makes a transition from a gapped to non-gapped state as a function of the phase differences in the system, the latter effectively playing the role of quasiparticle momenta in conventional topological matter. We here determine the proximity gap phase diagram of diffusive n-terminal Josephson junctions ( ∈ N n ), both numerically and analytically, by identifying a class of solutions to the Usadel equation at zero energy in the full proximity effect regime. We present an analytical equation which provides the phase diagram for an arbitrary number of terminals n. After briefly demonstrating the validity of the analytical approach in the previously studied 2-and 3-terminal cases, we focus on the 4-terminal case and map out the regimes where the electronic excitations in the system are gapped and non-gapped, respectively, demonstrating also in this case full agreement between the analytical and numerical approach.The interest in topological quantum phases of matter has grown steadily in recent years, and the fundamental importance of this topic in physics was recently recognized by Thouless, Haldane, and Kosterlitz being awarded the 2016 Nobel prize in physics for their contribution to this field. So far, specific material classes such as telluride-based quantum wells (HgTe, CdTe), bismuth antimony (Bi 1−x Sb x ) and bismuth selenide (Bi 2 Se 3 ) have received the most attention in the pursuit of symmetry-protected topological phases and excitations 1-4 . However, it was recently proposed 5 that similar physics could be obtained using conventional superconducting materials. More specifically, by using multiterminal Josephson junctions, the authors of ref. 5 showed that it was possible to create an artificial topological material displaying Weyl singularities under appropriate conditions. In multiterminal Josephson junctions hosting well-defined Andreev bound states, the crossing of these states with the Fermi level has been shown to be analogous to Weyl points in 3D solids with the Andreev bound state taking on the role of energy bands and the superconducting phase differences corresponding to quasiparticle momenta. A considerable advantage in utilizing multiterminal Josephson junctions rather than 3D solids to study exotic phenomena such as Weyl singularities and topologically different phases is that the phase differences are much more easily controlled experimentally than the quasiparticle momenta.In order to probe electronic excitations with topological properties, a key goal is to map out the phase diagram of the system in terms of when it is gapped or not. A gapped system here means that there are no available excitations in a finite interval around the Fermi level. The reason for why this...

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“…While strong hints of MF physics have been highlighted in Ref. [Mourik et al, 2012], other recent articles [Churchill et al, 2013;Linder et al, 2010;Kells et al, 2012;and Sun and Shah, 2015] offer alternative interpretation of the observed zero bias anomaly in terms of Kondo physics. Therefore an unambiguous "smokinggun" experimental proof of the presence of MFs still has to come.…”

Section: B Diffusive Limit: Weak Anti-localizationmentioning

confidence: 99%

Quantum transport in Rashba spin–orbit materials: a review

2015

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In this review article we describe spin-dependent transport in materials with spin-orbit interaction of Rashba type. We mainly focus on semiconductor heterostructures, however we consider topological insulators, graphene and hybrid structures involving superconductors as well. We start from the Rashba Hamiltonian in a two dimensional electron gas and then describe transport properties of two- and quasi-one-dimensional systems. The problem of spin current generation and interference effects in mesoscopic devices is described in detail. We address also the role of Rashba interaction on localisation effects in lattices with nontrivial topology, as well as on the Ahronov-Casher effect in ring structures. A brief section, in the end, describes also some related topics including the spin-Hall effect, the transition from weak localisation to weak anti localisation and the physics of Majorana fermions in hybrid heterostructures involving Rashba materials in the presence of superconductivity.

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General framework for transport in spin-orbit-coupled superconducting heterostructures: Nonuniform spin-orbit coupling and spin-orbit-active interfaces

Cited by 29 publications

References 107 publications

Magnetoanisotropic Andreev Reflection in Ferromagnet-Superconductor Junctions

Magnetoanisotropic Andreev Reflection in Ferromagnet-Superconductor Junctions

Analytically determined topological phase diagram of the proximity-induced gap in diffusive n-terminal Josephson junctions

Quantum transport in Rashba spin–orbit materials: a review

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