Interface structure of a topological insulator/superconductor heterostructure

Abstract

The construction of topological insulator/superconductor heterostructures attracts a lot of interest because of its potential to realize artificial topological superconductors hosting Majorana fermions. By means of molecular beam epitaxy, high-quality thin films of a topological insulator, Bi _2 Se _3 , can be grown on a superconductor substrate, 2H-NbSe _2 (0001), with an atomically smooth interface. To ascertain the atomic structure of the Bi _2 Se _3 /NbSe _2 heterostructure, the initial growth stage was investigated with a scanning tunneling microscope (STM). In the growth process, we found that Bi atoms were first deposited to form a single Bi(110) bilayer, which is revealed to stand nearly freely on the NbSe _2 surface and exhibits various moiré patterns. In the formation of the first quintuple layer of Bi _2 Se _3 by co-depositing Bi and Se atoms, the Bi(110) bilayer transits to a BiSe interfacial layer, which effectively reduces the large lattice mismatch between Bi _2 Se _3 and NbSe _2 . Based on atomic-resolution STM images and first-principles calculations, a NaCl-type structural model is proposed for the BiSe interfacial layer, on which Bi _2 Se _3 thin films grow well in a layer-by-layer mode.

Keywords

• topological insulator
• interface structure
• scanning tunneling microscope