Importance of interactions for the band structure of the topological Dirac semimetal Na_3Bi

摘要

We experimentally measure the band dispersions of topological Dirac semimetal Na_3Bi using Fourier-transform scanning tunneling spectroscopy to image quasiparticle interference on the (001) surface of molecular-beam epitaxy-grown Na_3Bi thin films. We find that the velocities for the lowest-lying conduction and valence bands are 1.6 × 10~6 ms_(-1) and 4.2 × 10~5 ms~(-1) respectively, significantly higher than previous theoretical predictions. We compare the experimental band dispersions to the theoretical band structures calculated using an increasing hierarchy of approximations of self-energy corrections due to interactions: generalized gradient approximation (GGA). meta-GGA, Heyd-Scuseria-Emzerhof 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 electronic structure of this Na_3Bi, and are likely the origin of the high velocity. The electron velocity is consistent with recent experiments on ultrathin Na_3Bi and also may explain the ultrahigh carrier mobility observed in heavily electron-doped Na_3Bi.