Local moments coupled to a strongly correlated electron chain

A one-dimensional model Hamiltonian that is motivated by the recent discovery of the heavy-fermion behavior in the cuprates of the Nd₂CuO₄ type is studied. It consists of t-J interacting conduction electrons coupled to a lattice of localized spins through a Kondo exchange term JK. Exact diagonalization and density-matrix renormalization-group methods are used. The latter method is generalized to arbitrary densities. At half filling, a spin gap opens for all JK>0. Away from half filling it is shown that, at strong JK, the ground state is an unsaturated ferromagnet. At weak JK the system is in a paramagnetic phase with enhanced Ruderman-Kittel-Kasuya-Yosida (RKKY) correlations. The importance of self-screening of the local moments in the depletion regime is discussed. We argue that these findings transcend the specifics of the model.