Over the last decade, the search for the topological superconducting (TSC) phase has attracted a great deal of attention because of both the elegant physics of the subject and its potential application in topological quantum computations. The TSC phase has been proposed to be present in hybrid structures where a topological insulator (TI) film is proximally coupled to a conventional s-wave superconductor [1]. In the past few years, we employed molecular beam epitaxy (MBE) to synthesize a series of TI-based heterostructures, including TI/superconductor [e.g., Bi₂Se₃/monolayer NbSe₂] and TI/non-superconducting material with interfacial superconductivity [e.g., (Bi,Sb)₂Te₃/FeTe and Cr-doped (Bi,Sb)₂Te₃/FeTe]. For Bi₂Se₃/monolayer NbSe₂ heterostructures, we found that the in-plane upper critical magnetic field of the superconducting Bi₂Se₃/monolayer NbSe₂ heterostructures is greatly reduced when the Rashba-type bulk conduction bands and surface states emerge, implying the crossover from the Ising- to Rashba-type superconductivity [2]. For (Bi,Sb)₂Te₃/FeTe and Cr-doped (Bi,Sb)₂Te₃/FeTe heterostructures, we found that interface-induced superconductivity emerges [3,4]. These TI/non-superconducting material heterostructures with interfacial superconductivity may also host the TSC phase because it fulfills the two essential ingredients of TSC, i.e. topological and superconducting orders [1]. The MBE-grown (Bi,Sb)₂Te₃/FeTe and Cr-doped (Bi,Sb)₂Te₃/FeTe heterostructures with atomically sharp interfaces will advance the fundamental inquiries into Majorana physics in hybrid devices and may provide an alternative approach for the exploration of the TSC phase.

References:

[1] Fu et al, Phys. Rev. Lett. 100, 096407(2008) ;

[2] Yi et al, Nature Mater. 21, 1366(2022) ;

[3] Yi et al, Nature Commun. (2023, under review) ;

[4] Yi et al, Science (2023, under review).