Abstract
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 that 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 fewer constraints on device geometry compared to previous devices that require external magnetic fields.
Highlights
Topological superconductivity has been predicted to appear in one-dimensional spin-orbit coupled semiconductors proximitized by an s-wave superconductor
We show that the combined superconducting and exchange proximity effects induced by the coupling to a spin-split Sc cannot induce, alone, a topological transition in the Sm
We have demonstrated that a spin-split superconductor cannot induce, alone, topological superconductivity in a spin-orbit coupled semiconductor by the combined superconducting and magnetic proximity effect
Summary
Topological superconductivity has been predicted to appear in one-dimensional spin-orbit coupled semiconductors proximitized by an s-wave superconductor. In these systems, an external magnetic field causes the gap to close. The system behaves as a spinless p-wave superconductor and Majorana bound states appear at the edges of the system. These states have been proposed to be used for topological quantum computation [3,4]. Different hybrid semiconductor–superconductor (Sm–Sc) platforms have been proposed to exhibit topological superconductivity, such as proximitized nanowires [5], selective-area-grown wires [6], and two-dimensional electron gas (2DEG) systems [7,8,9,10]
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