Moir\'e pattern formation in epitaxial growth on a covalent substrate: Sb on InSb(111)A

TL;DR

This study demonstrates the formation of moiré patterns in ultrathin Sb films on covalent InSb(111)A substrates, revealing unstrained growth and persistent topological surface states despite lattice mismatch.

Contribution

It shows that covalent substrates can host unstrained, moiré-patterned ultrathin Sb films with preserved topological properties, expanding understanding of moiré heterostructures beyond van der Waals materials.

Findings

Moiré patterns form in Sb films on covalent InSb(111)A despite lattice mismatch.

First Sb layer grows unstrained and azimuthally aligned.

Topological surface states persist down to low film thicknesses.

Abstract

Structural moir\'e superstructures arising from two competing lattices may lead to unexpected electronic behavior, such as superconductivity or Mottness. Most investigated moir\'e heterostructures are based on van der Waals (vdW) materials, as strong interface interactions typically lead to the formation of strained films or regular surface reconstructions. Here we successfully synthesize ultrathin Sb films, that are predicted to show thickness-dependent topological properties, on semi-insulating InSb(111)A. Despite the covalent nature of the substrate surface, we prove by scanning transmission electron microscopy (STEM) that already the first layer of Sb atoms grows completely unstrained, while azimuthally aligned. Rather than compensating the lattice mismatch of -6.4% by structural modifications, the Sb films form a pronounced moir\'e pattern as we evidence by scanning tunneling microscopy (STM) topography up to film thicknesses of several bilayers. Our model calculations based on density functional theory (DFT) assign the moir\'e pattern to a periodic surface corrugation. In agreement with DFT predictions, irrespective of the moir\'e modulation, the topological surface state known on thick Sb film is experimentally confirmed to persist down to low film thicknesses, and the Dirac point shifts towards lower binding energies with decreasing Sb thickness.