Quantum ground state control in superconductor-silicene structures: 0- π transitions, φ0 -junctions, and Majorana bound states

Abstract

We demonstrate theoretically that proximity-induced superconductivity in silicene offers the possibility to exert strong quantum ground state control. We show that electrically controlled 0-π transitions occur in Josephson junctions in the presence of an exchange field due to the buckling of the silicene lattice. We also discover that zigzag-oriented interfaces, featuring intervalley scattering, cause a ϕ0 state with an applied electric field. Finally, we demonstrate that Majorana bound states along the silicene edge are tunable via the edge orientation, electric, and in-plane spin exchange fields.PACS numbers: 74.50.+r, 74.45.+c, 73.61.Wp, 71.10.Pm The discovery of new low-dimensional materials, where the electron bands have topological properties, has attracted a large amount of interest in recent years. A particularly intriguing material is silicene [1], which consists of an atomically thin, buckled layer of Si atoms arranged in a honeycomb lattice. This material has theoretically been shown to host both different topological phases and has individually tunable mass gaps for each spin σ at each valley η [2-5]. These properties make silicene ideal for envisaging various types of device functionality related to both spintronics and valleytronics, a quest also significantly fueled by its compatibility with existing Si semiconductor technology. On the experimental side, silicene has already been studied on metallic substrates, including ZrB 2 [6] and notably Ag(111) [7][8][9], as well as for nonmetallic hosts, where a Si nanosheet grown on MoS 2 bulk crystals has recently been reported [10].A particularly exciting prospect is to consider the manifestation of superconducting correlations in silicene, with the unique properties of silicene likely leading to an advanced interplay between spintronics and superconductivity [11]. Recent experimental progress has enabled the study of superconductivity in atomically thin materials, such as in graphene [12][13][14] and transition metal dichalcogenides [15,16], through the proximity effect from external superconductors. Motivated by this, we set out to determine how superconductivity is manifested in silicene, especially focusing on the external control of unusual phenomena via an electric field.We demonstrate that proximity-induced superconductivity in silicene allows for a strong quantum ground state control. By creating superconductor-ferromagnetsuperconductor (SFS) Josephson junctions in bulk silicene, we find that the exchange field in the F region gives rise to electrically controlled 0-π transitions, due to the buckling of the silicene lattice. We also discover that zigzag-oriented SF interfaces, which host notable intrinsic intervalley scattering, result in an exotic ϕ 0 state, directly tunable by electric field. Finally, we demonstrate that the existence of Majorana bound states (MBS) at SF junctions on silicene edges is controlled by edge orientation and the strength of electric and in-plane exchange fields.First, we compute the supercurrent in bulk silicene S...

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Multiple odd-frequency superconducting states in buckled quantum spin Hall insulators with time-reversal symmetry

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