We study the two-dimensional periodic Anderson model at half filling using quantum Monte Carlo (QMC) techniques. The ground state undergoes a magnetic order-disorder transition as a function of the effective exchange coupling between the conduction and localized bands. Low-lying spin and charge excitations are determined using the maximum entropy method to analytically continue the QMC data. At finite temperature we find a competition between the Kondo effect and antiferromagnetic order which develops in the localized band through Ruderman-Kittel-Kasuya-Yosida interactions. PACS numbers: 75.20.Hr, 75.30.Et, 75.30.Mb, 75.40.Mg The periodic Anderson model (PAM) [1]describes a localized f band of strongly correlated electrons hybridized with a d band of free conduction electrons. As the temperature, filling, and Hamiltonian parameters are varied, there is a competition between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction [2] and the Kondo effect [3]. The RKKY interaction favors ordering the magnetic moments of the localized f band, while the Kondo effect screens the localized magnetic moments and quenches the magnetic interaction through the formation

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Using quantum Monte Carlo, we study the evolution of pseudogaps in the spectral weight function for a half-filled two-dimensional Hubbard model as a function of temperature and coupling constant. The formation of pseudogaps at finite temperature can be used to distinguish between three regimes: (1) a strong-coupling Mott-Hubbard regime, characterized by a pseudogap which persists even at high ternperatures; (2) a weak-coupling spin-density-wave regime, characterized by the absence of a pseudogap at any finite temperature; and (3) an intermediate-coupling regime with mixed behavior, characterized by a pseudogap that appears at a finite temperature.

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