Spin pumping in an altermagnet/normal-metal bilayer

Altermagnetism is a subclass of antiferromagnetism that features spin -polarized electron bands of a nonrelativistic origin despite the absence of net magnetization in the material. We here theoretically study spin pumping from an altermagnetic insulator into a normal metal. The symmetry properties of the lattice and spin order of the altermagnet alter the magnon dispersion compared to a conventional square lattice antiferromagnet. We find that for a homogeneous magnetic field, the spin pumping current is the same as that of a regular antiferromagnet. If, however, the magnetic field becomes spatially dependent, we predict that the altermagnetic order will leave a unique fingerprint on the spin pumping behavior when the orientation of the spatial modulation does not align with the high -symmetry paths of magnon degeneracy in the altermagnet. This demonstrates that altermagnets can be used for terahertz spin pumping purposes with novel behavior, distinguishing them from their regular antiferromagnet counterparts.