Molecular Doping the Topological Dirac Semimetal Na₃Bi across the Charge Neutrality Point with F4-TCNQ

We perform low-temperature transport and high-resolution photoelectron spectroscopy on 20 nm thin film topological Dirac semimetal Na₃Bi grown by molecular beam epitaxy. We demonstrate efficient electron depletion ∼10¹³ cm^-2 of Na₃Bi via vacuum deposition of molecular F4-TCNQ without degrading the sample mobility. For samples with low as-grown n-type doping (1 × 10¹² cm^-2), F4-TCNQ doping can achieve charge neutrality and even a net p-type doping. Photoelectron spectroscopy and density functional theory are utilized to investigate the behavior of F4-TCNQ on the Na₃Bi surface.