Exotic Spin-Orbit Torques in Chiral Tellurium

Tellurium has a chiral helical structure, which breaks the inversion symmetry and results in a momentum-dependent radial spin texture at the Fermi level. With a charge current applied along the chirality direction, the Fermi level will be shifted and spins of electrons will be polarized either parallel or anti-parallel to the current direction depending on the handedness of the Te chirality. We are studying this chirality-induced spin polarizations by using spin-torque ferromagnetic resonance to observe the spin-orbit torques generated from single-crystalline Te flakes. We deposited a 10-nm Permalloy (Py; Ni₈₀Fe₂₀) layer and used ion-milling and lithography to integrate Te/Py heterostructure into a coplanar waveguide for radio frequency (rf) measurements. We then applied GHz rf currents through Te/Py devices and collect a dc mixing voltage (V_mix) due to the mixing of anisotropic magnetoresistance of Py and rf current. The characteristics of spin-orbit torque components generated by Te flakes can be obtained by studying the dependence of V_mix as a function of applied magnetic field direction, and by analyzing the angular dependence of the voltages, we do find large spin torques generated by spins polarized along the current (chirality) direction, which is a direct consequence of the chiral structure of Te.