3D Topological Semimetal Phases of Strained $\alpha$-Sn on Insulating Substrate

TL;DR

This study demonstrates the growth of high-quality strained $ ext{α}$-Sn layers on insulating substrates and characterizes their topological Dirac and Weyl semimetal phases using various experimental techniques, revealing their potential for topological electronics.

Contribution

It reports the first successful growth of high-mobility $ ext{α}$-Sn on insulating substrates and provides a comprehensive experimental and theoretical analysis of its topological semimetal phases.

Findings

High-quality $ ext{α}$-Sn layers grown on insulating substrates with high electron mobility.

Identification of Dirac and Weyl semimetal phases induced by strain and magnetic field.

Observation of negative longitudinal magnetoresistance and $ ext{π}$ Berry phase confirming topological properties.

Abstract

$\alpha$-Sn is an elemental topological material, whose topological phases can be tuned by strain and magnetic field. Such tunability offers a substantial potential for topological electronics. However, InSb substrates, commonly used to stabilize $\alpha$-Sn allotrope, suffer from parallel conduction, restricting transport investigations and potential applications. Here, the successful MBE growth of high-quality $\alpha$-Sn layers on insulating, hybrid CdTe/GaAs(001) substrates, with bulk electron mobility approaching 20000 cm$^2$V$^{-1}$s$^{-1}$ is reported. The electronic properties of the samples are systematically investigated by independent complementary techniques, enabling thorough characterization of the 3D Dirac (DSM) and Weyl (WSM) semimetal phases induced by the strains and magnetic field, respectively. Magneto-optical experiments, corroborated with band structure modeling, provide an exhaustive description of the bulk states in the DSM phase. The modeled electronic structure is directly observed in angle-resolved photoemission spectroscopy, which reveals linearly dispersing bands near the Fermi level. The first detailed study of negative longitudinal magnetoresistance relates this effect to the chiral anomaly and, consequently, to the presence of WSM. Observation of the $\pi$ Berry phase in Shubnikov-de Haas oscillations agrees with the topologically non-trivial nature of the investigated samples. Our findings establish $\alpha$-Sn as an attractive topological material for exploring relativistic physics and future applications.