Tilting spin by light without SOC

Nonlinear optics goes to nonrelativistic regime in noncollinear magnetic configurations

Conventional spin orbit torque largely relies on the spin-orbit coupling (SOC) effect in its material platforms. Hence, it is usually limited to compose heavy elements in order to achieve strong enough SOC, so that the spin torque effect can be measured. We investigate this long standing problem in the view point of recently developed spin group theoretical approach, and we realized that, if the spin equilibrium configuration can be canted, especially noncollinear frustrated, then the SOC effect can be eliminated. In this sense, it is the exchange field energy that governs the torque magnitude, which might be 2-3 orders stronger than the SOC induced effect. In order to illustrate this process, we use density matrix perturbative theory to give an expression on how to express the nonlinear optical effect on spin torque, and uncover its underlying band geometry feature. Then we adopt our developed theory in Kagome lattices, to show that a moderate light field could generate about 30 T effective magnetic field, yielding a 0.1 rad disturbance on the spin direction.

See our work that just appeared in Physical Review Letters, at https://journals.aps.org/prl/abstract/10.1103/vcvp-w5fd. Our paper has been suggested as Editors’ Suggestion, to highlight on the homepage of PRL.