Quantum Monte Carlo simulations of the degenerate single-impurity Anderson model

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Abstract
We present results of quantum Monte Carlo simulations of the degenerate, single-impurity, Anderson model. Using maximum-entropy methods, we performed the analytic continuation of the imaginary-time Green’s functions produced by these simulations to obtain their real-frequency, single-particle, spectral densities for degeneracies of N=2, 4, and 6. Incorporating higher degeneracies into the model enables us, on the one hand, to compare Monte Carlo results with the self-consistent large-N approximation (NCA) and numerical-renormalization-group calculations (NGR) and, on the other hand, to bring the models closer to the physical systems. The low temperatures reached in our calculations are comparable to, or even lower than, the corresponding Kondo temperatures. The NCA and NRG calculations were found to show qualitatively good agreement with our results: the Kondo temperature increases with increasing degeneracy, and the amplitude of the side peaks in the spectral density decreases as degeneracy increases while the half-width of these peaks increases.