Experimental and Theoretical Electronic Structure and Symmetry Effects in Ultrathin NbSe2 Films

TL;DR

This study combines experimental ARPES measurements and theoretical calculations to explore how the electronic structure and symmetry of NbSe2 change as the material transitions from monolayer to multilayer films, revealing fundamental dimensional effects.

Contribution

It provides a detailed analysis of the electronic structure and symmetry effects in ultrathin NbSe2 films, highlighting differences between monolayer and bilayer configurations through combined experimental and theoretical approaches.

Findings

Significant changes in electronic band structure between monolayer and bilayer NbSe2.

Inversion symmetry is preserved in bilayer but not in monolayer NbSe2.

Dimensional effects influence the physical properties of NbSe2 films.

Abstract

Layered quasi-two-dimensional transition metal dichalcogenides (TMDCs), which can be readily made in ultrathin films, offer excellent opportunities for studying how dimensionality affects electronic structure and physical properties. Among all TMDCs, NbSe2 is of special interest; bulk NbSe2 hosts a charge-density-wave phase at low temperatures and has the highest known superconducting transition temperature, and these properties can be substantially modified in the ultrathin film limit. Motivated by these effects, we report herein a study of few-layer NbSe2 films, with a well-defined single-domain orientation, epitaxially grown on Gallium Arsenide (GaAs). Angle-resolved photoemission spectroscopy (ARPES) was used to determine the electronic band structure and the Fermi surface as a function of layer thickness; first-principles band structure calculations were performed for comparison. The results show interesting changes as the film thickness increases from a monolayer (ML) to several layers. The most notable changes occur between a ML and a bilayer, where the inversion symmetry in bulk NbSe2 is preserved in the bilayer but not in the ML. The results illustrate some basic dimensional effects and provide a basis for further exploring and understanding the properties of NbSe2.