Affiliated project

PhD student: Arnold Kole

Project Leader: Zeila Zanolli

Topological Superconductivity from First-Principles

In recent years there has been an increased interest in materials with topological properties (QuMat Pillar 1). These materials are characterised by a topological phase, which is separated from the normal phase by a discontinuous transformation. Topological phases and their related properties are therefore protected from disorder. Topological superconductors are a subclass of topological materials where a superconducting material exhibits a topological phase (QuMat Pillar 1+3). They might exhibit exciting new forms of physics such as edge states that behave like Majorana fermions.[1] One route to topological superconductivity could be by creating hybrid structures that combine s-wave superconductivity with spin-orbit coupling and magnetism.[1] Examples include structures where chains of magnetic atoms (Fe, Mn) are put on top of superconducting subtrates (Nb, Re) or Van der Waals heterostructures of superconductors (NbSe2) and two-dimensional magnetic materials (CrX3 where X=Cl,Br,I). Experiments show in-gap states in these materials which might be a signature of topological superconductivity.[2-4] Attempts have been made to explain these experiments using theoretical models, but a treatment that combines superconductivity with the full complexity of the electronic state of these systems is still missing. We have recently implemented an approach to describe superconductivity through the Bogoliubov-deGennes formalism in the Density Functional Theory code SIESTA.[5,6] The advantage of this unified approach is that material specific properties are treated accurately, such as the gap anisotropy for bulk Niobium. We use this state-of-the-art method to understand the physics behind these in-gap states and help elucidate their origin. A better understanding will allow us to make predictions about new materials that can host these states and perhaps eventually allows us to tune their properties.

[1] M. Sato et al., Reports on Progress in Physics 80: 076501 (2017)
[2] L. Schneider et al., Nat. Com. 11: 4707 (2020)
[3] L. Schneider et al., Nature Nanotechnology 17: 384 (2022)
[4] S. Kezilebieke et al., Nature 588: 424–28 (2020)
[5] J. M. Soler et al., J. Phys.: Condens. Matter 14: 2745–2779 (2002)
[6] R. Reho et al., in preparation (2023)

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