Selective control of surface spin current in topological pyrite-type OsX2 (X\u2009=\u2009Se, Te) crystals

Yuefeng Yin,Nikhil V Medhekar,Michael S Fuhrer

doi:10.1038/s41535-019-0186-8

Abstract

Topological materials host robust surface states that could form the basis for future electronic devices. As such states have spins that are locked to the momentum, they are of particular interest for spintronic applications. Understanding spin textures of the surface states of topologically nontrivial materials, and being able to manipulate their polarization, is therefore essential if they are to be utilized in future technologies. Here we use first-principles calculations to show that pyrite-type crystals OsX2 (X = Se, Te) are a class of topological materials that can host surface states with spin polarization that can be either in-plane or out-of-plane. We show that the formation of low-energy states with symmetry-protected energy- and direction-dependent spin textures on the (001) surface of these materials is a consequence of a transformation from a topologically trivial to nontrivial state, induced by spin orbit interactions. The unconventional spin textures of these surface states feature an in-plane to out-of-plane spin polarization transition in the momentum space protected by local symmetries. Moreover, the surface spin direction and magnitude can be selectively filtered in specific energy ranges. Our demonstration of a new class of topological materials with controllable spin textures provides a platform for experimentalists to detect and exploit unconventional surface spin textures in future spin-based nanoelectronic devices.

Highlights

These materials have the potential of exhibiting exotic spin-dependent transport properties, such as inverse spin Hall effect and spin-transfer torque on the surface states,[11,12] which can be beneficial for the development of spintronics and spin detection devices.[13,14]
Each class of topological materials possesses unique spin textures associated with their surface states and spin orbital coupling (SOC).[15,16]
Our results show that the lowest conduction band and neighboring valence bands for OsSe2 and OsTe2 are completely gapped along high symmetry lines, providing a possible venue for the emergence of nontrivial surface states between them

Summary

Introduction

Materials with nontrivial topological properties provide a rich playground for discovering unconventional fermions as well as unveiling novel physical phenomena such as giant magnetoresistance and superconductivity.[1,2] Over the last few years, topological states of matter have been revealed in a diverse spectrum of electronic structures from insulators[3] to semimetals[4,5] and metals.[6,7] Several strategies have been proposed to effectively predict new materials with nontrivial topology by combining the knowledge of dimensionality, crystal symmetry and band theory.[2,8] In particular, seeking materials that can demonstrate highly orientational and controllable spin structures is rapidly emerging as an active area of research.[9,10] These materials have the potential of exhibiting exotic spin-dependent transport properties, such as inverse spin Hall effect and spin-transfer torque on the surface states,[11,12] which can be beneficial for the development of spintronics and spin detection devices.[13,14]Each class of topological materials possesses unique spin textures associated with their surface states and spin orbital coupling (SOC).[15,16] In topological insulators (TIs), the spin textures of the surface states exhibit a strong spin-momentum locking behavior, where the direction of the spin of a Dirac fermion is locked perpendicular to its momentum,[17,18] typically lying in the plane of the surface. Given the The orbital character of the surface bands shows a further splitting symmetry of the crystal, the (001) surface of OsSe2 can have three possible surface terminations: Se–Se terminated, Se terminated of Os t2g and Os eg states as well as change of energy ordering compared to the bulk electronic states (see Fig. S3).

Results

Conclusion