Spatial Charge Inhomogeneity and Defect States in Topological Dirac Semimetal Thin Films

TL;DR

This study maps potential fluctuations in topological Dirac semimetal Na3Bi thin films, revealing minimal charge inhomogeneity and defect states that influence surface electronic properties, advancing understanding of topological materials.

Contribution

It provides the first detailed mapping of charge inhomogeneity and defect states in TDS Na3Bi thin films, highlighting reduced potential fluctuations and defect-induced resonances.

Findings

Potential fluctuations are significantly smaller than room temperature.

Na vacancies create large, tunable resonances near the Dirac point.

Charge inhomogeneity is comparable to high-quality graphene on h-BN.

Abstract

The close approach of the Fermi energy EF of a Dirac semimetal to the Dirac point ED uncovers new physics such as velocity renormalization,1,2,3 and the Dirac plasma 4,5 at |EF -ED| < kBT, where kBT is the thermal energy. In graphene, substrate disorder drives fluctuations in EF. Three-dimensional topological Dirac semimetals (TDS)6,7 obviate the substrate, and should show reduced EF fluctuations due to better metallic screening and higher dielectric constants. Here we map the potential fluctuations in TDS Na3Bi using a scanning tunneling microscope. The rms potential fluctuations are significantly smaller than room temperature ({\Delta}EF,rms = 4-6 meV = 40-70 K) and comparable to the highest quality graphene on h-BN;8 far smaller than graphene on SiO2,9,10 or the Dirac surface state of a topological insulator.11 Surface Na vacancies produce a novel resonance close to the Dirac point with surprisingly large spatial extent and provides a unique way to tune the surface density of states in a TDS thin-film material.