Theory of charge and spin pumping in atomic-scale spiral magnets

Abstract

An Archimedean screw is a classical pump that exploits the equivalence of rotation and translation in helices. Similarly, a spin spiral texture can pump charge and spin by rotating at a frequency 𝜔. In the present paper, we study these pumping phenomena within a microscopic quantum model by both perturbation theory and numerical simulations. Inside the spiral region, the spin polarization and charge current are linear in 𝜔 whereas the spin current is 𝜔 2 for small 𝜔. We find that the charge current is related to the mixed momentum-phason Berry phase, which can be viewed as a novel approximate realization of a Thouless pump. It is nearly quantized in spirals with short pitch 𝜆 but decays with 𝜆 −1 for longer pitches, unlike true Thouless pumps or Archimedean screws. Moreover, we study the onset of non-adiabaticity (large 𝜔), the impact of attached non-magnetic or magnetic contacts, and the real-time evolution of the transport observables. Finally, we analyze the effects of disorders which, surprisingly, might enhance the spin current but suppress the charge current.

Helitronics as a potential building block for classical and unconventional computing

“…These states, which can be viewed as a labyrinth of one-dimensional topological solitons, are coming back into the focus of spintronic research due to their unique symmetry. They have been shown to work as emergent inductors [18][19][20], lead to non-reciprocal charge and spin transport [21][22][23][24], or may actively pump spin and charge as Archimedean screws [25][26][27]. Moreover, they can serve as a non-trivial background for other topological excitations such as skyrmions [28][29][30] or dislocations [31][32][33][34].…”