Large Bandgap Observed on the Surfaces of EuZn2As2 Single Crystals

TL;DR

This study reveals large, defect-sensitive bandgaps on EuZn2As2 surfaces using STM/S and DFT, providing insights into its topological properties and surface heterogeneity effects.

Contribution

It combines experimental STM/S data with DFT calculations to analyze surface bandgaps and defect effects in EuZn2As2, advancing understanding of its topological characteristics.

Findings

Large (~1.5 eV) surface bandgaps observed at 77 K.

Bandgap size varies with local defects and heterogeneity.

Zn vacancies and substitutions influence the surface electronic structure.

Abstract

EuM2As2 (M = Zn, Cd, In, Sn etc.) is an excellent material system for studying topological properties, which can be easily tuned by magnetism involved. Theoretical calculations predict gapped and flat bands in EuZn2As2 but gapless structure in EuCd2As2. In this work, low-temperature (77 K) cleaved EuZn2As2 crystals are studied using scanning tunneling microscopy/spectroscopy (STM/S) and density functional theory (DFT) calculations. Defects-induced local density of states (LDOS) modification with a triangular shape helps identify the surface terminations: Eu versus AsZn surface. While large bandgaps (~1.5 eV at 77 K) are observed on both pristine surfaces, the bandgap width is found to be very sensitive to local heterogeneity, such as defects and step edges, with the tendency of reduction. Combining experimental data with DFT simulations, we conclude that the modified bandgap in the heterogeneous area arises from Zn vacancies and/or substitution by As atoms. Our investigation offers important information for reevaluating the electron topology of the EuM2As2 family.