The ground state of dilute Tm systems is degenerate

The ground state of the appropriate generalization of the impurity Anderson model for valence fluctuations between two realistic Tm+2 and Tm+3 configurations is obtained in the atomic, narrow band limit, using the Lanczos' method. This limit describes the strong-coupling fixed point of renormalization-group treatments for intermediate valence and Kondo impurities. The resulting ground state is highly-degenerate and contains states of total angular momentum 0, 3/2, 2, 5/2, 4 and 9/2. The crystal electric field or an applied magnetic field should split the degeneracy favouring the magnetic states. As found in TmSe, the Tm magnetic moment is anomalously small. (Author)