Large magnetoresistance and superconductivity in \u03b1-gallium single crystals

Bin Chen,Jinhu Yang,Yuxing Zhou,Jianhua Du,Chunqiang Xu,Xu Duan,Minghu Fang,Yukun Zhang,Zhengcai Xia,Liyao Zhang,Chao Cao,Meng Wei,Jianhui Dai,Hangdong Wang

doi:10.1038/s41535-018-0114-3

Abstract

Topological metals, including Dirac and Weyl semimetals, represent a wide class of quantum materials with non-trivial electronic band structures. The essential properties of Dirac or Weyl fermions, including light effective mass and high mobility, have been observed in a number of semimetal compounds, which in turn exhibit large positive magnetoresistances. Here, we report an unexpected observation of all these properties in α-gallium (α-Ga) single crystals, a pure metal that is in the liquid phase at room temperature and ambient pressure. Based on systematical transport measurements, α-Ga single crystal is found to exhibit large magnetoresistance, reaching about 1.66 × 106 per cent at 2 K in a magnetic field of 9 T. At low temperatures the de Haas–van Alphen and Shubinikov de Hass quantum oscillations show ultrahigh mobility and very small cyclotron effective mass for charge carriers, together with a non-trivial Berry phase. Combined with first-principle band structure calculations, these properties demonstrate α-Ga as a rare topological pure metal. Furthermore, superconductivity with Tc of ~0.9 K is confirmed by both specific heat and resistivity measurements. These findings suggest that α-Ga is a unique pure metal displaying both non-trivial topological and superconducting properties.

Highlights

The recent discoveries of topological semimetals (TSMs) have stimulated intense interest in condensed matter physics and material science.[1,2,3,4,5,6] The typical Dirac semimetals such as Na3Bi1,7 and Cd3As2,2 for instance, have four-fold degenerate band crossing points in the momentum space
The type-II Dirac semimetal PdTe2 is a superconductor with Tc = 2 K, the MR is ~900% at 0.36 K under the magnetic field of 30 T with the effect mass of 0.13m0.52 A large unsaturated MR is discovered in WTe23 at ambient pressure, but the MR is quickly suppressed under high pressure, and a superconducting state appears at the critical pressure of 10.5 GPa.[21,53]
Large single crystals of gallium were grown from the oriented seeds

Summary

INTRODUCTION

The recent discoveries of topological semimetals (TSMs) have stimulated intense interest in condensed matter physics and material science.[1,2,3,4,5,6] The typical Dirac semimetals such as Na3Bi1,7 and Cd3As2,2 for instance, have four-fold degenerate band crossing points in the momentum space. More generic topological materials should include topological metals, the bulk metals with topologically protected surface states or band crossing points Such metals can be viewed as doped TSMs or doped topological insulators, or the mixtures with additional metallic bands, though a thorough classification has yet to be reached.[27,28] Among all these topological materials the two dimensional graphene is known as the simplest Dirac semimetal consisting of a single layer of pure carbons.[29,30]. The lambda-like peaks indicate a superconducting phase below 0.9 K. e Resistance as a function of temperature at various magnetic fields (0, 0.5, 1.5, 2, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 10, 15, 20, 50, and 100 mT). Superconductivity in the same α-Ga single crystals is confirmed by the specific heat capacity measurement and by an improved resistivity measurement All these findings show the coexistence of topological phase and superconducting properties in such a simple pure metal

RESULTS

15 K 17 K 18 K 20 K 25 K 30 K

Findings

DISCUSSION