Scrutinizing a superconductor-topological insulator interface as a platform for topological superconductivity

Abstract

Interfacing a topological insulator (TI) with an s-wave superconductor (SC) is a promising material platform that offers the possibility to realize a topological superconductor through which Majorana-based topologically protected qubits can be engineered. In our computational study of the prototypical SC/TI interface between Nb and Bi2Te3, we identify the benefits and possible bottlenecks of this potential Majorana material platform. Bringing Nb in contact with the TI film induces charge doping from the SC to the TI, which shifts the Fermi level into the TI conduction band. For thick TI films, this results in band bending leading to the population of trivial TI quantum-well states at the interface. In the superconducting state, we uncover that the topological surface state experiences a sizable superconducting gap-opening at the SC/TI interface, which is furthermore robust against fluctuations of the Fermi energy. We also show that the trivial interface state is only marginally proximitized, potentially obstructing the realization of Majorana-based qubits in this material platform.

Atomic Diffusion-Induced Polarization and Superconductivity in Topological Insulator-Based Heterostructures

“…In addition, no significant charge transfer between the xPBT and TI phases is observed in our calculated band structures (Figure S12 in the Supporting Information). This indicates that detrimental band bending effects unveiled in our earlier work on the Nb/Bi 2 Te 3 interface 56 are absent, which makes this S− TI interface a good candidate to engineer a topological superconductor.…”

“…The JuKKR code also comes with an extension to the Kohn−Sham−Bogoliubov−de Gennes method, which allows to calculate superconducting properties. 56,64 The series of DFT calculations in this study are orchestrated with the help of the AiiDA-KKR 65,66 and AiiDA-FLEUR 67,68 plugins to the AiiDA infrastructure. 69 This has the advantage that the full data provenance (including all values of numerical cutoffs and input parameters to the calculation) is automatically stored in compliance with the FAIR principles of open research data.…”

Density-functional description of materials for topological qubits and superconducting spintronics

“…The different λ i are allowed to vary in the different sites i of a computational unit cell which enables the description of inhomogeneous systems consisting of superconductors and non-superconductors such as magnets, 19,22 normal metals, 14,15,18,33 or topological insulators. 16,17 In the KKR formalism it is straight-forward to include the BdG formalism where using multiple-scattering theory the Green's function for the KS-BdG Hamiltonian, Eq. ( 1), is found.…”

“…This is particularly the case for disordered systems where the second approach is favorable as a compromise between numerical demand and flexibility. It was successfully used to study conventional s-wave superconductors, [10][11][12][13] heterostructures of s-wave superconductors and nonsuperconductors, [14][15][16][17][18] or impurities embedded into superconductors. [19][20][21][22] In this work we focus on recent developments in the KS-BdG method using the parameter-based approach.…”