Hidden spin polarization in TaTe$_2$, applications in spintronics*

We investigate the relationship between the hidden spin polarization and underlying crystal symmetries in TaTe$_2$ using first-principles calculations. Time reversal symmetry combined with bulk inversion symmetry prohibits the presence of a net k-dependent spin-polarization, but does not forbid the presence of a local spin-polarization [1]. Here, we report the presence of such a 'hidden' spin-polarization in TaTe$_2$, a centrosymmetric layered material. On application of an electric field, a net spin polarization is generated in the Te layers, which can result in a local spin-orbit torque (SOT) when interfaced with a ferromagnet. Interestingly, we find that the nature of the SOT changes from Rashba-like to Dresselhaus-like as TaTe$_2$ undergoes a transition from the high symmetry P-3m1 phase to the room temperature C12/m1 phase. Further, we find that the Dresselhaus-like torque can reverse its sign within the C12/m1 space group when the local symmetries are altered. Finally, we compare our first principle calculations to the experimental observation of temperature-dependent Dresselhaus-like SOT in C12/m1 TaTe2/Ni_{80}Fe_{20} heterostructures.

[1] X. Zhang et al., Nature Physics 10, 387, (2014)