Pressure-induced superconductivity and topological phase transitions in the topological nodal-line semimetal SrAs3

Erjian Cheng,Zhiqiang Zou,Xufeng Kou,Yong Zhang,Na Yu,Zhenhai Yu,Xia Wang,Yanfeng Guo,Lin Wang,Chuchu Zhu,Dongzhe Dai,Wenge Yang,Darren C Peets,Shiyan Li,Weiwei Zhao,Xianbiao Shi,Hao Su,Wei Xia,Limin Yan

doi:10.1038/s41535-020-0240-6

Abstract

Topological nodal-line semimetals (TNLSMs) are materials whose conduction and valence bands cross each other, meeting a topologically protected closed loop rather than discrete points in the Brillouin zone (BZ). The anticipated properties for TNLSMs, include drumhead-like nearly flat surface states, unique Landau energy levels, special collective modes, long-range Coulomb interactions, or the possibility of realizing high-temperature superconductivity. Recently, SrAs3 has been theoretically proposed and then experimentally confirmed to be a TNLSM. Here, we report high-pressure experiments on SrAs3, identifying a Lifshitz transition below 1 GPa and a superconducting transition accompanied by a structural phase transition above 20 GPa. A topological crystalline insulator (TCI) state is revealed by means of density functional theory (DFT) calculations on the emergent high-pressure phase. As the counterpart of topological insulators, TCIs possess metallic boundary states protected by crystal symmetry, rather than time reversal. In consideration of topological surface states (TSSs) and helical spin texture observed in the high-pressure state of SrAs3, the superconducting state may be induced in the surface states, and is most likely topologically nontrivial, making pressurized SrAs3 a strong candidate for topological superconductor.

Highlights

In recent years, topological semimetals including Dirac, Weyl, and nodal-line semimetals have been theoretically predicted and experimentally verified, opening a new field in condensed-matter physics in which novel properties and new applications can arise from spin-polarized states with unique band dispersion[1,2,3]
From an X-ray rocking curve of the (002) Bragg peak, a full width at half maximum (FWHM) of 0.04° indicates the high quality of the SrAs3 single crystal grown from Bi flux, while a broader FWHM of 0.15° for the SF sample suggests lower quality
Searching for Majorana fermions has been fueled by the prospect of using their non-Abelian statistics for robust quantum computation, and they can be realized as a bound state at zero energy, i.e., Majorana bound states, in the vortex core of a TSC27,28

Summary

Introduction

Topological semimetals including Dirac, Weyl, and nodal-line semimetals have been theoretically predicted and experimentally verified, opening a new field in condensed-matter physics in which novel properties and new applications can arise from spin-polarized states with unique band dispersion[1,2,3]. Unlike the discrete points in momentum space in Dirac or Weyl semimetals[2,3], the band crossings in nodal-line semimetals can form closed loops inside the BZ4; a nodal chain consisting of several connected loops[5]; or an extended line traversing the entire BZ6 These one-dimensional nodal curves are topologically protected by certain discrete symmetries, for example mirror reflection, time-reversal, or spin-rotation symmetries[2,3]. The nodal-line structure is expected to have several intriguing properties[3], such as unique Landau energy levels[7], special collective modes[8], long-range Coulomb interactions[9], or drumhead-like nearly flat surface states[10,11], which can be considered a higher-dimensional analog of the flat band on the zigzag edge of graphene[3]. These drumhead states may host interesting correlation effects, and even offer the possibility of realizing high-temperature superconductivity[12]

Methods

Results

Conclusion