Researchers from the RIKEN Center for Emergent Matter Science, together with their colleagues, have shown the conversion of a spin current into a rotating charge current vortex using numerical simulations.

This new approach can contribute to the emergence of energy efficient spintronic devices, as it helps to convert between electrical current vortices and a spin current and vice versa. The team came up with the idea of ​​exploiting the Rashba effect – an unusual phenomenon that was discovered in 1959. It occurs on some surfaces or interfaces between two materials where the atomic structure is no longer symmetrical. The Rashba effect causes the spin and the orbital motion of an electron to interact.

“The spin-orbit coupling is a relativistic effect that mixes the spin and the orbital motion of electrons,” explains RIKEN's Sadamichi Maekawa. “The Rashba coupling is important in oxide interface structures and in some two-dimensional materials where it creates various novel topological phenomena useful in spintronics.”

Maekawa and his co-workers used large-scale computer simulations to model what would happen if a spin current was injected into a rashba material through a point-sized electrical contact. The team looked at an arrangement where the direction of the spins is perpendicular to the rashba material, and their simulations showed that this created a rotating current of charge. This is a consequence of the constitution that the angular momentum must always be maintained, and thus the transition converts the fed-in spin angular momentum largely into the orbital angular momentum of the vortex.

“In electronics, the dynamics of electrons are everything: diffusive flow as well as hydrodynamic or turbulent motion,” says Maekawa. In spintronics, however, only the diffusive electron flow has been considered so far. “With the generation of charge current vortices, our work shows the possibility of hydrodynamic spintronics, which extends spintronics to include the hydrodynamic regime of electrons.”

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