‘‘Anomalous fixed point behavior’’ of two Kondo impurities: A reexamination

We consider the existence of ``anomalous fixed point behavior'' for the Kondo two-impurity Hamiltonian. This ``anomalous'' behavior is predicted by calculations which use the ``energy-independent coupling constants'' (ECC) approximation. Using well-controlled quantum Monte Carlo methods without the ECC approximation, we find no evidence for ``anomalous'' behavior. We then show that the ECC approximation is, in general, either inconsistent or uninteresting. These results together strongly suggest that the predicted ``anomalous'' behavior of two Kondo impurities is simply the result of an unphysical approximation rather than an intrinsic property of the model itself.