Single-hole dynamics in the half-filled two-dimensional Kondo-Hubbard model

We consider the Kondo lattice model in two dimensions at half filling. In addition to the Fermionic hopping integral t and the superexchange coupling J the role of a Coulomb repulsion U in the conduction band is investigated. We find the model to display a magnetic order-disorder transition in the U-J plane with a critical value of J c which is decreasing as a function of U. The single-particle spectral function A(k,ω) is computed across this transition. For all values of J>0, and apart from shadow features present in the ordered state, A(k,ω) remains insensitive to the magnetic phase transition with the first low-energy hole states residing at momenta k=(′π,′π). As J →0 the model maps onto the Hubbard Hamiltonian. Only in this limit does the low-energy spectral weight at k=(′π,′π) vanish such that the lowest energy hole states reside at wave vectors on the magnetic Brillouin-zone boundary. Thus we conclude that (i) the local screening of impurity spins determines the low-energy behavior of the spectral function and (ii) one cannot deform continuously the spectral function of the half-filled Hubbard model at J = 0 to that of the Kondo insulator at J>J c . Our results are based on both TO Quantum Monte-Carlo simulations and a bond-operator mean-field theory.