Phase-controllable nonlocal spin polarization in proximitized nanowires

Zhang, Xianpeng; Golovach, Vitaly N.; Giazotto, Francesco; Bergeret, F. S.

doi:10.1103/physrevb.101.180502

Cited by 10 publications

(6 citation statements)

References 75 publications

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“…1 (b), have shown no signatures of topological phases. This behavior is in contrast with expectations that the main effect of MIs is to induce an exchange field in the Sm [21].…”

Section: Introductioncontrasting

confidence: 99%

Topological superconductivity in semiconductor-superconductor-magnetic insulator heterostructures

Maiani,

Souto,

Leijnse

et al. 2020

Preprint

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Hybrid superconductor-semiconductor heterostructures are promising platforms for realizing topological superconductors and exploring Majorana bound states physics. Motivated by recent experimental progress, we theoretically study how magnetic insulators offer an alternative to the use of external magnetic fields for reaching the topological regime. We consider different setups, where: (1) the magnetic insulator induces an exchange field in the superconductor, which leads to a splitting in the semiconductor by proximity effect, and (2) the magnetic insulator acts as a spin-filter tunnel barrier between the superconductor and the semiconductor. We show that the spin splitting in the superconductor alone cannot induce a topological transition in the semiconductor. To overcome this limitation, we propose to use a spin-filter barrier which enhances the magnetic exchange and provides a mechanism for a topological phase transition. Moreover, the spin-dependent tunneling introduces a strong dependence on the band alignment, which can be crucial in quantum-confined systems. This mechanism opens up a route towards networks of topological wires with less constraints on device geometry as compared to previous devices which require external magnetic fields.

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“…1 (b), have shown no signatures of topological phases. This behavior is in contrast with expectations that the main effect of MIs is to induce an exchange field in the Sm [21].…”

Section: Introductioncontrasting

confidence: 99%

Topological superconductivity in semiconductor-superconductor-magnetic insulator heterostructures

Maiani,

Souto,

Leijnse

et al. 2020

Preprint

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“…First, an energy splitting of the superconducting coherence peak appears in the Al [Fig. 2(b) bottom panel], which is of the order of ∼ 0.06 meV, in agreement with recent theoretical and experimental results on Al/EuS junctions [32][33][34][35]. This agreement without any fine tuning of the parameters in our model is encouraging about its validity.…”

supporting

confidence: 89%

Tunable proximity effects and topological superconductivity in ferromagnetic hybrid nanowires

et al. 2021

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Hybrid semiconducting nanowire devices combining epitaxial superconductor and ferromagnetic insulator layers have been recently explored experimentally as an alternative platform for topological superconductivity at zero applied magnetic field. In this proof-of-principle work we show that the topological regime can be reached in actual devices depending on some geometrical constraints. To this end, we perform numerical simulations of InAs wires in which we explicitly include the superconducting Al and magnetic EuS shells, as well as the interaction with the electrostatic environment at a self-consistent mean-field level. Our calculations indicate that the topological phase is achieved in significant portions of the phase diagram only in configurations where the Al and EuS layers overlap on some wire facet due to their rather local induced proximity effects. Moreover, we find that the spin polarization induced directly in the semiconductor by the EuS is much stronger than the one induced indirectly through the superconductor. Finally, we comment on how the topological phase can be tuned and optimized using external gates.

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“…We consider the zero-temperature case. As it is well know, quasiclassical GFs only describes the physics close to the Fermi surface and, hence, to obtain the total spin density one has to add the Pauli paramagnetic term [45,47]. Namely, the Pauli paramagnetic contribution of each magnetic impurity is given by /π in units of h/2 [12].…”

Section: Junctions Of Collinear Acsmentioning

confidence: 99%

Spectral properties of Andreev crystals

2021

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We present an exhaustive study of Andreev crystals (ACs)-quasi-one-dimensional superconducting wires with a periodic distribution of magnetic regions. The exchange field in these regions is assumed to be much smaller than the Fermi energy. Hence, the transport through the magnetic region can be described within the quasiclassical approximation. In the first part of the paper, by assuming that the separation between the magnetic regions is larger than the coherence length, we derive the effective nearest-neighbor tight-binding equations for ACs with a helical magnetic configuration. The spectrum within the gap of the host superconductor shows a pair of energy-symmetric bands. By increasing the strength of the magnetic impurities in ferromagnetic ACs, these bands cross without interacting. However, in any other helical configuration, there is a value of the magnetic strength at which the bands touch each other, forming a Dirac point. Further increase of the magnetic strength leads to a system with an inverted gap. We study junctions between ACs with inverted spectrum and show that junctions between (anti)ferromagnetic ACs (always) never exhibit bound states at the interface. In the second part, we extend our analysis beyond the nearest-neighbor approximation by solving the Eilenberger equation for infinite ACs and junctions between semi-infinite ACs with collinear magnetization. From the obtained quasiclassical Green functions, we compute the local density of states and the local spin polarization in anti-and ferromagnetic ACs. We show that these junctions may exhibit bound states at the interface and fractionalization of the surface spin polarization.

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Phase-controllable nonlocal spin polarization in proximitized nanowires

Cited by 10 publications

References 75 publications

Topological superconductivity in semiconductor-superconductor-magnetic insulator heterostructures

Topological superconductivity in semiconductor-superconductor-magnetic insulator heterostructures

Tunable proximity effects and topological superconductivity in ferromagnetic hybrid nanowires

Spectral properties of Andreev crystals

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