Theory of spin torque in Weyl semimetals with magnetic texture*

We theoretically study the spin-transfer torque, a fundamental physical quantity to understand the electrically-induced dynamics of magnetic texture. We calculate the electrically-induced non-equilibrium spin density of a Weyl semimetal (WSM) and obtain the analytical expression of the spin torque corresponding to a non-adiabatic spin-transfer torque. Importantly, the strength of the obtained spin torque outstrips that of conventional ferromagnetic metals when magnetization varies steeply. Furthermore, due to the suppression of longitudinal conductivity in this regime, the dissipation due to Joule heating for the spin-transfer torque is smaller than that in conventional ferromagnetic metals. We also analyze the dynamics of the domain walls driven using the spin-transfer torque and find that the velocity of the domain wall is one order of magnitude greater than that of a conventional ferromagnetic nanowire. Consequently, the fast-control of domain walls can be achieved with smaller dissipation in the WSM. Therefore, the WSM can be a new candidate for application to spintronics devices such as the racetrack memory.