Quantum critical point in a periodic Anderson model

We investigate the symmetric Periodic Anderson Model (PAM) on a three-dimensional cubic lattice with nearest-neighbor hopping and hybridization matrix elements. Using Gutzwiller's variational method and the Hubbard-III approximation (which corresponds to the exact solution of an appropriate Falicov-Kimball model in infinite dimensions) we demonstrate the existence of a quantum critical point at zero temperature. Below a critical value $V_c$ of the hybridization (or above a critical interaction $U_c$) the system is an {\em insulator} in Gutzwiller's and a {\em semi-metal} in Hubbard's approach, whereas above $V_c$ (below $U_c$) it behaves like a metal in both approximations. These predictions are compared with the density of states of the $d$- and $f$-bands calculated from Quantum Monte Carlo and NRG calculations. Our conclusion is that the half-filled symmetric PAM contains a {\em metal-semimetal transition}, not a metal-insulator transition as has been suggested previously.Comment: ReVteX, 10 pages, 2 EPS figures. Minor corrections made in the text and in the figure captions from the first version. More references added. Accepted for publication in Physical Review

Regulation of susceptibility and resistance to experimental allergic encephalomyelitis by neuroendocrine and immune factors

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