Superconducting state versus excitonic condensate in Kondo lattices

In the strongly correlated antiferromagnetic lattices, the coupling of magnons and electrons (or holes) forms composite states whose spectra are depending on the interplay of the Kondo exchange and the Heisenberg interaction within a localized spin field. These composite states can constitute electron-hole pairs, and, in certain conditions, the gas of these pairs can present the characteristic features of an insulating excitonic condensate. Another possibility, propitiated by these composite states in other next conditions, is the appearance of antiferromagnetic heavy-fermion superconductivity. The competition between these two antithetic condensed coherent states, superconductor and insulating excitonic condensate, can occur for realistic values of governing parameters of the Kondo/Heisenberg Hamiltonian, the appearance of a quantum criticality being possible. The model presented in this paper is in reasonable agreement with other previous analyses, and represents a new route for studying these competitive collective states that can appear in these strongly correlated materials. © 2006 The American Physical Society.