Heavy – Fermion Semiconductor Behaviour and Phase Transition of CeCu2Si2 in the Single Site Impurity Anderson Model.

We investigate the electronic properties of CeCu2Si2 in the low temperature regime using the Exact-Diagonalization technique. This technique allows the study of the physics of strongly correlated electron systems. We show that when the hybridization term in the Single Site Impurity Anderson Model (SIAM) is increased: (1) there is a smooth phase transition from an antiferromagnetic phase to a ferromagnetic phase and (2) there is a semiconductor gap ∆ between the singlet state and triplet states energies as the lattice sites and dimensions is increasing. The basic features of this theory are in qualitative agreement with the experimentally observed heavy-fermion semiconductor of some rare-earth compounds.