Strong Intrinsic Spin Hall Effect in the TaAs Family of Weyl Semimetals

Abstract

Since their discovery, topological insulators have been expected to be ideal spintronic materials owing to the spin currents carried by surface states with spin-momentum locking. However, the bulk doping problem remains an obstacle that hinders such application. In this work, we predict that a newly discovered family of topological materials, the Weyl semimetals, exhibits large intrinsic spin Hall effects that can be utilized to generate and detect spin currents. Our ab initio calculations reveal a large spin Hall conductivity that is comparable to that of 4d and 5d transition metals. The spin Hall effect originates intrinsically from the bulk band structure of Weyl semimetals, which exhibit a large Berry curvature and spin-orbit coupling, so the bulk carrier problem in the topological insulators is naturally avoided. Our work not only paves the way for employing Weyl semimetals in spintronics, but also proposes a new guideline for searching for the spin Hall effect in various topological materials.Topological insulators (TIs) are characterized by metallic surface states inside the bulk energy gap [1,2], in which the spin and momentum are locked together with a vortex-like spin texture. Because counterpropagating surface states carry opposite spins, if charge current is introduced into a nominally perfect TI (with no bulk conductivity), the current should be fully spinpolarized. Thus, TIs have been considered as excellent materials for generating spin current, and this expectation has stimulated several recent experimental studies of the spin Hall effect (SHE) in TIs such as Bi 2 Se 3 [3] and (Bi 0.5 Sb 0.5 ) 2 Te 3 [4] that demonstrated highly efficient spin current conversion. However, the unavoidable bulk carrier problem remains an obstacle to widespread application of TIs. Interestingly, an exotic type of topological semimetal, the Weyl semimetal (WSM), exhibits similar spin-momentum locking in both the bulk and topological surface states [5][6][7][8][9]. Therefore, we are motivated to study the SHE, which refers to transverse spin current generation by a longitudinal charge current and is essential for state-of-the-art spintronic applications [10], in this new family of topological materials.In a WSM, the conduction and valence bands cross each other linearly in the three-dimensional (3D) momentum space near the Fermi energy through nodal points, called Weyl points, in a 3D analog of the band structure of graphene. Because of strong spin-orbit coupling (SOC), the Weyl points act as sources or sinks of the Berry curvature [11], which characterizes the entanglement between the conduction and valence bands. Here, we naturally expect the existence of a large SHE intrinsically originating from the bulk band structure, because the SHE is derived from the spinmomentum locking and Berry curvature of the electronic bands [12,13]. Recently, the first family of WSMs was predicted [14,15] and discovered by angle-resolved photoemission spectroscopy [16][17][18][19] in the transition-metal * yan@cpfs.mpg.de TABLE I. Nonz...

Observation of nodal line in non-symmorphic topological semimetal InBi

“…The first kind of TNS is where the conduction and the valence band touch in zero-dimension forming either quadruply degenerate points (topological Dirac semimetal) [3][4][5][6] or pairs of doubly degenerate points with opposite chirality (topological Weyl semimetal) [7,8]. Apart from being protected due to the topological nature, these points have bands disperse through them linearly in three-dimensional (3D) momentum space, which brings interesting phenomena such as unusually high carrier mobility [9,10], large intrinsic spin Hall effect [11], giant diamagnetism [12], and chiral anomaly in magnetoresistance [13,14]. Recent experimental works have successfully demonstrated the existence of 3D Dirac point in materials e.g.…”

Topological Weyl semimetals in the chiral antiferromagnetic materials Mn3Ge and Mn3Sn

“…In a WSM, the conduction and valence bands cross each other linearly through nodes called Weyl points. Between a pair of Weyl points with opposite chiralities (sink or source of the Berry curvature) [4], the emerging Berry flux can lead to the anomalous Hall effect (AHE) [30], as observed in GdPtBi [27,28], and an intrinsic spin Hall effect (SHE), as predicted in TaAs-type materials [31], for systems without and with time-reversal symmetry, respectively. Herein, we raise a simple recipe to search for WSM candidates among materials that host strong AHE or SHE.…”

Multiple Types of Topological Fermions in Transition Metal Silicides

“…For example, the Majorana-like excitations are detected in superconducting heterostructures [3][4][5][6]; the Dirac [7][8][9][10][11][12] and Weyl [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] fermions are observed in some compounds. These quasiparticles in solid states are not only important for basic science, but also show great potential for practical applications on new devices [30,31].…”