Prof. Alexey Kovalev (Nebraska Center for Materials and Nanoscience)
"Spin and energy currents in ferromagnets and antiferromagnets with Dzyaloshinskii-Moriya interactions"
Understanding spin transport in nanostructures is a long-standing problem in condensed matter physics and it involves understanding the behavior of spin ensembles which are quantum in nature. Apart from being fundamental, such studies are also of great practical interest for spintronic applications. Recently, spin transport through antiferromagnetic insulating systems has attracted renewed interest due to availability of new experiments. New experimental techniques related to the spin Seebeck, spin Hall, and inverse spin Hall effects make it possible to test new theoretical predictions in the context of spin currents. In addition to angular momentum, such spin currents also carry energy making such studies relevant for the field of spincaloritronics. In this work we study spin and energy currents induced by temperature gradients and/or magnetization dynamics. In the latter case, we predict that magnon motive force can lead to temperature dependent, nonlinear chiral damping in both conducting and insulating ferromagnets. We estimate that this damping can significantly influence the motion of skyrmions and domain walls at finite temperatures. We also find that in systems with low Gilbert damping moving chiral magnetic textures and resulting magnon motive forces can induce large spin and energy currents in the transverse direction. We also study the magnon bands in ferromagnetic and antiferromagnetic insulators and predict that a temperature gradient can induce a magnon-mediated intrinsic torque and a transverse spin current in magnets with nontrivial magnon Berry curvature. With the help of a microscopic linear response theory of nonequilibrium magnon-mediated torques and spin currents, we identify the interband and intraband components that manifest in magnets with Dzyaloshinskii?Moriya interactions. To illustrate and assess the importance of such e?ects, we apply our theory to the magnon-mediated spin Nernst and torque responses of topological magnon insulators.