Abstract
The verification of topological superconductivity has become a major experimental challenge. Apart from the very few spin-triplet superconductors with p-wave pairing symmetry, another candidate system is a conventional, two-dimensional (2D) s-wave superconductor in a magnetic field with a sufficiently strong Rashba spin-orbit coupling. Typically, the required magnetic field to convert the superconductor into a topologically non-trivial state is however by far larger than the upper critical field Hc2, which excludes its realization. In this article, we argue that this problem can be overcome by rotating the magnetic field into the superconducting plane. We explore the character of the superconducting state upon changing the strength and the orientation of the magnetic field and show that a topological state, established for a sufficiently strong out-of-plane magnetic field, indeed extends to an in-plane field orientation. We present a three-band model applicable to the superconducting interface between LaAlO3 and SrTiO3, which should fulfil the necessary conditions to realize a topological superconductor.
Highlights
On the other hand, if the material provides a chiral band structure by itself, a conventional BCS superconductor with an s-wave order parameter can be topologically non-trivial as well
In our analysis of the topology upon rotating the magnetic field H into the plane, we include the Zeeman coupling of the electrons to the magnetic field, but neglect the orbital coupling. This approximation is well justified for the nearly in-plane field orientation on which we focus here; but orbital effects are necessarily important for the superconducting state in an out-of-plane magnetic field
The Rashba spin-orbit coupling (SOC) and the Zeeman coupling to the magnetic field H are combined into
Summary
The verification of topological superconductivity has become a major experimental challenge. As a candidate system, which can possibly fulfil the required conditions, we consider the metallic LaAlO3-SrTiO3 (LAO-STO) interface[18,19] For this system, several models are proposed for a topologically non-trivial superconducting state, which rely on an unconventional order parameter[20,21,22]. Assuming instead an s-wave pairing state, we demonstrate that a multi-band model involving the titanium t2g orbitals allows for a topologically non-trivial superconductor in a realistic parameter regime for the LAO-STO interface. We suggest that it may be achieved with the currently used experimental setups
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