First-principles Study Of Spin Hall Effect In The 5d Transition Metal Compound

In recent years,the spin Hall effect（SHE）attract much attention not only in condensed matter physics but also in the device applications of spintronics.Relying on SHE,people could generate pure spin current directly from charge current without the need of applying magnetic field or relying on magnetic materials.Therefore,this effect provides a promising way to exploit the spin degree of freedom in electronic devices,such as spin Hall effect transistor,all-electric spin field effect transistor,independent double gate field effect transistor,spin orbital torque devices,and so on.There are several mechanisms by which the SHE can be achieved,and they can be generally separated into two groups:extrinsic mechanisms and intrinsic mechanisms.Since the spin Hall conductivity（SHC）generated by the extrinsic mechanism depends on the impurities,defects,and so on,the SHE based on this mechanism is uncontrollable,so people mainly focus on the SHE with the intrinsic mechanism.Under the intrinsic mechanism,if the material’s SHC is larger,the spin current obtained will be larger with the same spin Hall angle（SHA,i.e.spin current conversion efficiency）.Therefore,searching for materials with large and stable intrinsic SHC has always been an important topic in the field of spintronics.Based on this,three types of 5d transition metal compound materials with large and stable SHC are proposed in this paper.The specific contents are summarized in the following three parts:It is generally believed that conductivity platform can only exist in insulator with topological nontrivial bulk occupied states.In this paper,we propose that SHC plateau can form in the Ta N series materials with triply degenerate points,so we take the experimentally synthesized Ta N as a prototype to study the intrinsic SHC.Our ab initio calculations predict that a nearly ideal SHC plateau with a width of 0.55 e V forms in the energy range of[-0.58,-0.03]e V for Ta N with hole doping,with an absolute maximum SHC of 439（/e）S/cm and a large SHA（-0.57）at-0.03 e V.The large SHC plateau and SHA makes Ta N to be excellent material to produce large and stable spin current when there is a thermal disturbance.With the help of a four-band k·p model,we prove that SHC plateau of Ta N series materials mainly comes from the localized SBC produced between|3/2,±3/2>and|1/2,±1/2>states.Using ab initio calculations,we also predict other Ta N family material Ta P,Ta As,Ta Sb,Ta Bi exhibits ideal SHC plateau.Using ab initio calculations,we have studied the SHE of the Hf Se family materials with the coexistence of triply degenerate nodal points and Weyl points.The experimentally synthesized Hf Se has an intrinsic SHC of-367（?/e）S/cm and a large intrinsic SHA of-0.55.It does not have the SHC plateau as the Ta N series materials with triply degenerate points,but its SHC is quasi-linear slowly changing with hole doping.The variation of SHC values for Hf Se is 7%/0.1e V.Its quasi-linear SHC with hole doping is mainly come from the SBC contribution of|3/2,±3/2>and|1/2,±1/2>states and Weyl points around Fermi level.We also discover that the other Hf Se family material,Hf S and Hf Te,exhibits similar quasi-linear slowly changing SHC,which is superior to the drastic SHC changes observed in most metallized materials when doped.The quasi-linear slowly changing SHC in Hf Se family materials is favorable for producing controllable spin current under hole doping.Using ab initio calculations,we predict hexagonal layered material Pt₂B exhibits a giant intrinsic SHE with the intrinsic SHC of 2159（?/e）S/cm and the SHC can reach 2274（?/e）S/cm if the material is doped to 0.04 e V above the intrinsic Fermi level.Furthermore,Pt₂B has giant SHC in the large energy range near the instrinsic Fermi level,which including the SHC is quasi-linear slowly change（with variation is 7%/0.1e V）in the energy range of[0.04,0.16]e V.Its occupied bands have local extreme values of annular distribution in any plane perpendicular to the high symmetry line K-H,and the large energy difference distribution between the occupied and unoccupied band near those local extreme values,resulting Pt₂B having giant SHC in the large energy range with doping.