Temperature Dependent n-p Transition of 3 Dimensional Dirac Semimetal Na$_3$Bi Thin Film

TL;DR

This study investigates the temperature-dependent electrical transport in Na$_3$Bi thin films, revealing a transition from electron-like to hole-like conduction around 200 K and highlighting the impact of electron-phonon scattering on mobility.

Contribution

The paper introduces a model accounting for electron-hole asymmetry in a Dirac semimetal, explaining the temperature dependence of Hall resistivity and mobility in Na$_3$Bi thin films.

Findings

Hall coefficient changes sign around 200 K

Hole mobility is about 7 times larger than electron mobility

Electron mobility decreases with increasing temperature due to phonon scattering

Abstract

We study the temperature dependence ($77$ K - $475$ K) of the longitudinal resistivity and Hall coefficient of thin films (thickness $20$ nm) of three dimensional topological Dirac semimetal Na$_3$Bi grown via molecular beam epitaxy (MBE). The temperature-dependent Hall coefficient is electron-like at low temperature, but transitions to hole-like transport around $200$ K. We develop a model of a Dirac band with electron-hole asymmetry in Fermi velocity and mobility (assumed proportional to the square of Fermi velocity) which explains well the magnitude and temperature dependence of the Hall resistivity. We find that the hole mobility is about $7$ times larger than the electron mobility. In addition, we find that the electron mobility decreases significantly with increasing temperature, suggesting electron-phonon scattering strongly limits the room temperature mobility.