Exact Results of Strongly Correlated Systems at Finite Temperature

Some rigorous conclusions of the Hubbard model, Kondo lattice model and periodic Anderson model at finite temperature are acquired employing the fluctuation-dissipation theorem and particle-hole transform. The main conclusion states that for the three models, the expectation value of ${\bf \tilde{S}}^2-{\bf \tilde{S}}^2_z$ will be of order $N_{\Lambda}$ at any finite temperature.