Abstract
We examine the doping effects in the two-dimensional periodic Anderson model using the determinant Quantum Monte Carlo (DQMC) method. We observe bound states around the Kondo hole site and find that the heavy electron states are destroyed at the nearest-neighbor sites. Our results show no clear sign of hybridization oscillation predicted in previous mean-field calculations. We further study the electron transport with increasing doping and as a function of temperature and obtain a critical doping xc ≈ 0.6 that marks a transition from the Kondo insulator regime to the single-ion Kondo regime. The value of xc is in good agreement with the predicted threshold for the site percolation. Our results confirm the percolative nature of the insulator-metal transition widely observed in doped Kondo insulators.
Highlights
Chemical substitution or doping of the magnetic ions (Ce, Yb, U, ...) by its nonmagnetic counterpart element (La, Th, Y, ...) gives rise to local vacancies of the magnetic f-moments and could cause dramatic changes in the ground state properties of heavy fermion compounds
We are able to reproduce the predicted bound states around the Kondo hole site obtained in previous mean-field calculations and find that the hybridized heavy electron states are destroyed in the neareast-neighbor sites
We further study the electronic transport with increasing doping and confirm the percolation transition from the Kondo insulator state in the dense Kondo lattice to the single-ion Kondo behavior in the diluted limit
Summary
We start with the following modified Hamiltonian for the periodic Anderson lattice,. H = −t ∑ij ,σ ci†σ c jσ + H.c. + ∑ V i,σ ci†σ f iσ + H.c. For large εfI , the local f-electron occupation is effectively empty or full, so the f-electron degree of freedom at the impurity site plays essentially no role in the simulation and we find no severe sign problem. The split of the resonance peak is a special feature of the Anderson lattice model and originates from the collective hybridization between the conduction band and the effective f-electron flat band near the Fermi energy. The local occupation of the conduction electrons, nIcσ , is strongly enhanced and increases rapidly with increasing V This may be understood if we integrate out the local f-electron degree of freedom at the impurity site. We obtain effectively a local attractive potential, δεcI ∝ − V2/ εfI , which tends to trap the conduction electrons on the Kondo hole site, causing the increase of nIcσ.
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