Magnetic impurities in an altermagnetic metal

Abstract

We study the physics of dilute magnetic impurities in a two-dimensional altermagnetic metal. For the single impurity case, although the spin degeneracy is broken in an altermagnetic metal, we show that the antiferromagnetic Kondo coupling still flows to the strong coupling regime at low energies in terms of the one-loop renormalization-group equation. Moreover, the Kondo temperature may be enhanced or reduced, depending on the band structure and the electron density. To study the ground-state properties, we employ the variational wavefunction approach. We find that the impurity spin is completely screened at long distances, in contrast to the usual antiferromagnet. The $d$-wave nature of the spin-split Fermi surfaces in an altermagnetic metal is reflected in the correlation between the impurity and conduction electron spins, which exhibits the $C_{4z}$ symmetry of the altermagnet at long distances. The spin correlation decays as $1/r^3$ at long distances, and its amplitude oscillates with four different periods due to the interference between the spin splitting Fermi surfaces. Moreover, the values of these periods depend on the direction of observation. Similar phenomena also occur in the RKKY interaction in an AM metal.