Importance of interactions for the band structure of the topological Dirac semimetal Na3Bi

TL;DR

This study measures the band structure of Na3Bi using advanced spectroscopy and compares it with various theoretical models, highlighting the importance of electron interactions in accurately predicting its high electron velocities and mobility.

Contribution

It demonstrates that sophisticated exchange-correlation models, especially GW, are essential for accurately describing Na3Bi's electronic structure, surpassing simpler DFT approaches.

Findings

Experimental electron velocities are higher than initial theoretical predictions.

Density functional theory underestimates electron velocities.

GW calculations align well with experimental results.

Abstract

We experimentally measure the band dispersions of topological Dirac semimetal Na3Bi using Fourier-transform scanning tunneling spectroscopy to image quasiparticle interference on the (001) surface of molecular-beam epitaxy-grown Na3Bi thin films. We find that the velocities for the lowest-lying conduction and valencebands are 1.6x10^6 m/s and 4.2x10^5 m/s respectively, significantly higher than previous theoreticalpredictions. We compare the experimental band dispersions to the theoretical band structures calculated usingan increasing hierarchy of approximations of self-energy corrections due to interactions: generalized gradientapproximation (GGA), meta-GGA, Heyd-Scuseria-Ernzerhof exchange-correlation functional (HSE06), and GW methods. We find that density functional theory methods generally underestimate the electron velocities. However, we find significantly improved agreement with an increasingly sophisticated description of the exchange and interaction potential, culminating in reasonable agreement with experiments obtained by the GW method. The results indicate that exchange-correlation effects are important in determining the electronicstructure of this Na3Bi, and are likely the origin of the high velocity. The electron velocity is consistent withrecent experiments on ultrathin Na3Bi and also may explain the ultrahigh carrier mobility observed in heavilyelectron-doped Na3Bi.