Topological electronic states in HfRuP family superconductors

Yuting Qian,Lingyuan Kong,Youguo Shi,Zhijun Wang,Simin Nie,Hong Ding,Tian Qian,Chen Fang,Changjiang Yi,Zhong Fang,Hongming Weng

doi:10.1038/s41524-019-0260-6

Abstract

Based on the first-principles calculations and experimental measurements, we report that the hexagonal phase of ternary transition metal pnictides TT’X (T=Zr, Hf; T’=Ru; X=P, As), which are well-known noncentrosymmetric superconductors with relatively high transition temperatures, host nontrivial bulk topology. Before the superconducting phase transition, we find that HfRuP belongs to a Weyl semimetal phase with 12 pairs of type-II Weyl points, while ZrRuAs, ZrRuP and HfRuAs belong to a topological crystalline insulating phase with trivial Fu-Kane {{mathbb{Z}}}_{2} indices but nontrivial mirror Chern numbers. High-quality single crystal samples of the noncentrosymmetric superconductors with these two different topological states have been obtained and the superconductivity is verified experimentally. The wide-range band structures of ZrRuAs have been identified by ARPES and reproduced by theoretical calculations. Combined with intrinsic superconductivity, the nontrivial topology of the normal state may generate unconventional superconductivity in both bulk and surfaces. Our findings could largely inspire the experimental searching for possible topological superconductivity in these compounds.

Highlights

1234567890():,; INTRODUCTION Topological insulators (TIs)[1,2] and semimetals[3,4,5,6,7] have received a tremendous amount of attention in the last decade due to the appearance of exotic properties, such as spin-momentum locked gapless surface state in TIs8,9, Fermi-arc states[10,11,12] and negative magnetoresistance in Weyl semimetals (WSMs)[7,13,14]. These insulators can be characterized by topological invariants/indices, like Fu-Kane Z2 indices[15] and mirror Chern numbers[16,17] for TIs and topological crystalline insulators (TCIs), respectively
In contrast to the point-like bulk Fermi surfaces of the type-I WSMs7,19–25, these type-II WSMs26–30 have both electron pockets and hole pockets touching at the Weyl points, resulting in various novel physical properties[31,32]
We conclude that the band inversion happens at the K point, which is supported by the theory of topological quantum chemistry[61,62]

Summary

Introduction

Topological insulators (TIs)[1,2] and semimetals[3,4,5,6,7] have received a tremendous amount of attention in the last decade due to the appearance of exotic properties, such as spin-momentum locked gapless surface state in TIs8,9, Fermi-arc states[10,11,12] and negative magnetoresistance in Weyl semimetals (WSMs)[7,13,14] These insulators can be characterized by topological invariants/indices, like Fu-Kane Z2 indices[15] and mirror Chern numbers[16,17] for TIs and topological crystalline insulators (TCIs), respectively.

Methods

Results

Conclusion