Double-sided van der Waals epitaxy of topological insulators across an atomically thin membrane

TL;DR

This paper demonstrates the double-sided epitaxy of van der Waals topological insulators on atomically thin membranes, enabling the creation of novel heterostructures and tunneling devices with preserved quantum properties.

Contribution

It introduces a method for growing vdW topological insulators on both sides of atomically thin membranes, expanding the possibilities for quantum heterostructures and tunneling applications.

Findings

Successful growth of Sb₂Te₃ and Bi₂Se₃ on both surfaces of 2D membranes

Fabrication of homo- and hetero- double-sided vdW TI tunnel junctions

Observation of energy-momentum-spin resonant tunnelling in devices

Abstract

Atomically thin van der Waals (vdW) films provide a novel material platform for epitaxial growth of quantum heterostructures. However, unlike the remote epitaxial growth of three-dimensional bulk crystals, the growth of two-dimensional (2D) material heterostructures across atomic layers has been limited due to the weak vdW interaction. Here, we report the double-sided epitaxy of vdW layered materials through atomic membranes. We grow vdW topological insulators (TIs) Sb$_2$Te$_3$ and Bi$_2$Se$_3$ by molecular beam epitaxy on both surfaces of atomically thin graphene or hBN, which serve as suspended 2D vdW "$\textit{substrate}$" layers. Both homo- and hetero- double-sided vdW TI tunnel junctions are fabricated, with the atomically thin hBN acting as a crystal-momentum-conserving tunnelling barrier with abrupt and epitaxial interface. By performing field-angle dependent magneto-tunnelling spectroscopy on these devices, we reveal the energy-momentum-spin resonant tunnelling of massless Dirac electrons between helical Landau levels developed in the topological surface states at the interface.