Electric and spin current vortices in altermagnets

TL;DR

This paper proposes a method to detect altermagnetic spin splitting through transport measurements using nonuniform electric fields, revealing swirling electric and spin current vortices as unique signatures of altermagnets.

Contribution

It introduces a novel approach to probe altermagnetic Fermi surfaces via nonuniform fields, predicting observable swirling currents in the Ohmic regime.

Findings

Swirling electric and spin currents depend on the orientation of altermagnetic lobes.

Vortices are detectable via magnetometry techniques.

Swirling currents are unique to altermagnets, not present in ferromagnets.

Abstract

Altermagnets constitute a class of collinear magnets with momentum-dependent spin splitting and vanishing net magnetization. Direct observation of the characteristic altermagnetic spin splitting, however, remains challenging. Indirect signatures can be obtained via transport studies, which so far have only considered homogeneous driving fields. We propose to leverage nonuniform electric fields and spin density gradients to probe the shape and the spin polarization of altermagnetic Fermi surfaces via transport measurements. By using both a semiclassical Boltzmann approach and a lattice Keldysh formalism, we show that altermagnets excite swirling electric and spin currents whose profiles depend on the relative orientation of altermagnetic lobes with respect to the sample boundaries. These currents can be measured via magnetometry techniques. Unlike previous proposals considering the hydrodynamic regime of transport, swirling currents are observed even in the Ohmic regime and rely exclusively on the altermagnetic spin splitting, with no swirls observed in ferromagnets. The electric and spin current vortices predicted here provide a different altermagnetic signature in an experimentally accessible setup.