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 Jc 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 →J0 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>Jc. Our results are based on both $T=0$ Quantum Monte-Carlo simulations and a bond-operator mean-field theory.