Local-moment formation in the periodic Anderson model with superconducting correlations

Abstract

We study local-moment formation in the presence of superconducting correlations among the f electrons in the periodic Anderson model. Local moments form if the Coulomb interaction $U>{U}_{\mathrm{cr}}.$ We find that ${U}_{\mathrm{cr}}$ is considerably stronger in the presence of superconducting correlations than in the nonsuperconducting system. Our study is done for various values of the f-level energy and electronic density. The smallest critical ${U}_{\mathrm{cr}}$ values occur for the case where the number of f electrons per site is equal to 1. In the presence of d-wave superconducting correlations we find that local-moment formation presents a quantum phase transition as function of pressure. This quantum phase transition separates a region where local moments and d-wave superconductivity coexist from another region characterized by a superconducting ground state with no local moments. We discuss the possible relevance of these results to experimental studies of the competition between magnetic order and superconductivity in ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}.$