Behavior of a magnetic impurity in small metallic systems

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Results of the present project are summarized as follows :1. We investigated the Kondo effect in two-dimensional disordered systems using a quantum Monte Carlo method. It was shown that the local magnetic moment is screened or unscreened by the spin of the conduction electron, depending on the position of a magnetic impurity. The correlation function between the local moment and the spin of the conduction electron was also calculated. Even when the local moment is completely screened, the ferromagnetic correlation in the vicinity of the local moment is suppressed due to randomness. When the screening is incomplete, the antiferromagnetic correlation in the vicinity of the local moment is strongly suppressed.2. The elementary excitation spectrums for the Anderson model and the orbitally degenerate Anderson model were investigated at finite temperatures using the Bethe ansatz solution. We calculated a crossover behavior of the elementary excitation spectrums between the mixedvalence regim … More e and the Kondo regime. We also calculated the elementary excitation spectrums in crystalline fields such as tetragonal field and cubic field. Results were discussed in connection with thermodynamic quantities.3. Critical properties of various one-dimensional spin-gapped systems in magnetic fields were investigated systematically by combining a numerical diagonalization method and finite-size-scaling analysis based on conformal field theory. We calculated magnetic-field dependence of the critical exponent of the spin correlation function. Using the numerical results, we discussed the experimental findings concerning the NMR relaxation rates of the S=1/2 two-leg ladder material and the Haldane-gap material in magnetic fields.4. Using the continued fraction method based on Lanczos algorithm, the dynamical structure factor of the S=1/2 bond-alternating chain with a next-nearest-neighbor interaction was calculated at the magnetization-plateau region. Results were discussed in comparison with the exact excitation spectrums of an effective Hamiltonian ; one-dimensional S=1/2XXZ model. Less