Proximity-Induced π Josephson Junctions in Topological Insulators and Kramers Pairs of Majorana Fermions

Constantin Schrade; A. A. Zyuzin; Jelena Klinovaja; Daniel Loss

doi:10.1103/PhysRevLett.115.237001

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Proximity-Induced π Josephson Junctions in Topological Insulators and Kramers Pairs of Majorana Fermions

Constantin Schrade, A. A. Zyuzin, Jelena Klinovaja, Daniel Loss

DOI 10.1103/PhysRevLett.115.237001 · Physical Review Letters

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Abstract

We study two microscopic models of topological insulators in contact with an s-wave superconductor. In the first model the superconductor and the topological insulator are tunnel coupled via a layer of randomly distributed scalar and of randomly oriented spin impurities. Here, we demonstrate that spin-flip tunneling dominates over the spin-conserving one. In the second model the tunnel coupling is realized by a spatially nonuniform array of single-level quantum dots with randomly oriented spins. We find that the tunnel region forms a π junction where the effective order parameter changes sign. Because of the random spin orientation, effectively both models exhibit time-reversal symmetry. The proposed π junctions support topological superconductivity without magnetic fields and can be used to generate and manipulate Kramers pairs of Majorana fermions by gates.