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

Abstract

Atomically thin van der Waals (vdW) films provide a material platform for the epitaxial growth of quantum heterostructures. However, unlike the remote epitaxial growth of three-dimensional bulk crystals, the growth of two-dimensional 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 Sb2Te3 and Bi2Se3 by molecular-beam epitaxy on both surfaces of atomically thin graphene or hexagonal boron nitride, which serve as suspended two-dimensional vdW substrate layers. Both homo- and hetero-double-sided vdW topological insulator tunnel junctions are fabricated, with the atomically thin hexagonal boron nitride acting as a crystal-momentum-conserving tunnelling barrier with abrupt and epitaxial interfaces. By performing field-angle-dependent magneto-tunnelling spectroscopy on these devices, we reveal the energy–momentum–spin resonance of massless Dirac electrons tunnelling between helical Landau levels developed in the topological surface states at the interfaces. Double-sided epitaxy of van der Waals materials through atomic membranes is demonstrated, enabling electrons to resonantly tunnel between aligned topological insulator surfaces with the conservation of energy, momentum and spin helicity.