Towards Weyltronics: Realization of epitaxial NbP and TaP Weyl Semimetal thin films

TL;DR

This paper reports the successful growth of epitaxial NbP and TaP Weyl semimetal thin films, demonstrating their topological surface states and electronic properties, which paves the way for device applications exploiting Weyl physics.

Contribution

First demonstration of epitaxial growth of NbP and TaP thin films with controlled electronic structure and topological surface states.

Findings

Epitaxial NbP and TaP films grown on MgO substrates.

Films exhibit topological surface states and linear dispersion bands.

Electronic transport dominated by holes and electrons with high mobility.

Abstract

Weyl Semimetals (WSMs), a recently discovered topological state of matter, exhibit an electronic structure governed by linear band dispersions and degeneracy (Weyl) points leading to rich physical phenomena, which are yet to be exploited in thin film devices. While WSMs were established in the monopnictide compound family several years ago, the growth of thin films has remained a challenge. Here, we report the growth of epitaxial thin films of NbP and TaP by means of molecular beam epitaxy. Single crystalline films are grown on MgO (001) substrates using thin Nb (Ta) buffer layers, and are found to be tensile strained (1%) and with slightly P-rich stoichiometry with respect to the bulk crystals. The resulting electronic structure exhibits topological surface states characteristic of a P-terminated surface and linear dispersion bands in agreement with the calculated band structure, and a Fermi-level shift of -0.2 eV with respect to the Weyl points. Consequently, the electronic transport is dominated by both holes and electrons with carrier mobilities close to 10^3 cm2/Vs at room-temperature. The growth of epitaxial thin films opens up the use of strain and controlled doping to access and tune the electronic structure of Weyl Semimetals on demand, paving the way for the rational design and fabrication of electronic devices ruled by topology.