PROTRACTED SCREENING IN THE PERIODIC ANDERSON MODEL

The asymmetric infinite-dimensional periodic Anderson model is examine d with a quantum Monte Carlo simulation. For small conduction band fil ling, we find a severe reduction in the Kondo scale, compared to the i mpurity value, as well as protracted spin screening consistent with so me recent controversial photoemission experiments. The Kondo screening drives a ferromagnetic transition when the conduction band is quarter filled and both the Ruderman-Kittel-Kasuya-Yosida (RKKY) and superexc hange favor antiferromagnetism. We also find RKKY-driven ferromagnetic and antiferromagnetic transitions.