Magnetic impurities in an altermagnetic metal

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 whether or not the Fermi level is close to the Van Hove singularity at zero altermagnetic coupling. 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.

The Fermi surface in an altermagnetic metal is split (left). Although a magnetic impurity in an altermagnetic metal is completely screened, the spin correlation between it and the conduction electrons exhibits nontrivial angular dependence (middle) ndue to the interference between spin-split Fermi surfaces. Similar behavior is also shown in the RKKY interaction (right).