Kekul\'e distortions in graphene on cadmium sulfide

TL;DR

This study demonstrates the formation of Kekul'e superlattices in graphene placed on cadmium sulfide surfaces, revealing modifications in electronic properties and spin-orbit coupling, supported by theoretical models and microscopy simulations.

Contribution

It introduces a method to create Kekul'e graphene superlattices on CdS surfaces and provides detailed theoretical and simulation insights into their structure and properties.

Findings

Kekul'e superlattices can be formed on graphene/CdS heterostructures.

Two types of Kekul'e superlattices, Kekul'e-O and Kekul'e-Y, are identified.

Spin-orbit coupling is present in these superlattices.

Abstract

The deposition of a two-dimensional material on the surface of a three-dimensional crystal can generate superlattices with electronic properties modified through the proximity spin-orbit effect. In this study, we found that Kekul\'e graphene superlattices are obtained by placing graphene on Cd-terminated (001)-(1$\times$1) cadmium sulfide (CdS) surface. From an effective model of Kekul\'e superlattices, which is corroborated by Density Functional Theory (DFT) calculations, we identified that the puckered surfqace of CdS modifies the on-site energies (staggered potential) and C-C bonds, giving rise to two possible $\sqrt{3} \times \sqrt{3}$ hexagonal superlattices, which are known as Kekul\'e-O graphene and Kekul\'e-Y with a quadratic band crossing point. Both Kekul\'e superlattices present spin-orbit coupling due to the interaction of graphene with the CdS surface. To guide the experimental realization of Kekul\'e superlattices based on graphene/CdS heterostructures, we simulate electron diffraction patterns, as well as images from High-Resolution Transmission Electron Microscopy (HRTEM), and Scanning Transmission Electron Microscopy in the mode of High Angle Annular Dark Field (STEM-HAADF).