Periodic Anderson model with correlated conduction electrons: variational and exact diagonalization study

TL;DR

This study explores how conduction electron interactions influence heavy-fermion and mixed-valence states in an extended periodic Anderson model using variational and exact diagonalization methods.

Contribution

It provides a comparative analysis of variational and exact methods on the extended model, revealing the impact of conduction electron interactions on heavy-fermion behavior.

Findings

Interaction widens the f-level energy range for heavy-fermion states.

U_d shifts the heavy-fermion regime above the conduction band.

Transition from Kondo to Mott insulator is robust at half-filling.

Abstract

We investigate an extended version of the periodic Anderson model (the so-called periodic Anderson-Hubbard model) with the aim to understand the role of interaction between conduction electrons in the formation of the heavy-fermion and mixed-valence states. Two methods are used: (i) variational calculation with the Gutzwiller wave function optimizing numerically the ground-state energy and (ii) exact diagonalization of the Hamiltonian for short chains. The f-level occupancy and the renormalization factor of the quasiparticles are calculated as a function of the energy of the f-orbital for a wide range of the interaction parameters. The results obtained by the two methods are in reasonably good agreement for the periodic Anderson model. The agreement is maintained even when the interaction between band electrons, U_d, is taken into account, except for the half-filled case. This discrepancy can be explained by the difference between the physics of the one- and higher dimensional models. We find that this interaction shifts and widens the energy range of the bare f-level, where heavy-fermion behavior can be observed. For large enough U_d this range may lie even above the bare conduction band. The Gutzwiller method indicates a robust transition from Kondo insulator to Mott insulator in the half-filled model, while U_d enhances the quasi-particle mass when the filling is close to half filling.