Magnetic impurity coupled to a strongly correlated electron system in two dimensions

Highly dispersive scattering from defects in noncollinear magnets

We demonstrate that pointlike defects in noncollinear magnets give rise to a highly dispersive structure in the magnon scattering, violating a standard paradigm of its momentum independence. For a single impurity spin coupled to a prototypical noncollinear antiferromagnet, we find that the resolvent is dominated by a distinct dispersive structure with its momentum dependence set by the magnon dispersion and shifted by the ordering vector. This feature is a consequence of umklapp scattering off the impurity-induced spin texture, which arises due to the noncollinear ground state of the host system. Detailed results for the staggered and uniform magnetization of this texture as well as the T matrix from numerical linear spin-wave theory are presented.

Susceptibility of the 2D spin-1 / 2 Heisenberg antiferromagnet with an impurity

We use a quantum Monte Carlo method (stochastic series expansion) to study the effects of a magnetic or nonmagnetic impurity on the magnetic susceptibility of the two-dimensional Heisenberg antiferromagnet. At low temperatures, we find a log-divergent contribution to the transverse susceptibility. We also introduce an effective few-spin model that can quantitatively capture the differences between magnetic and nonmagnetic impurities at high and intermediate temperatures.