Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.12: Poster

Saturday, March 5, 2005, 11:00–16:30, Poster TU C

Singular Dynamics of Underscreened Magnetic Impurity Models — •Winfried Koller, Alex C. Hewson, and Dietrich Meyer — Department of Mathematics, Imperial College London

We give a comprehensive analysis of the singular dynamics and of the low-energy fixed point of one-channel impurity s-d models with ferromagnetic and underscreened antiferromagnetic couplings. We use the numerical renormalization group (NRG) to perform calculations at T=0. The spectral densities of the one-electron Green’s functions and t-matrices are found to have very sharp cusps at the Fermi level (ω=0), but do not diverge. The approach of the Fermi level is governed by terms proportional to 1/ln2(ω/T₀) as ω→ 0. The scaled NRG energy levels show a slow convergence as 1/(N+C) to their fixed point values, where N is the iteration number and C is a constant dependent on the coupling J from which the low energy scale T₀ can be deduced. We calculate also the dynamical spin susceptibility, and the elastic and inelastic scattering cross-sections as a function of ω. The inelastic scattering goes to zero as ω→ 0, as expected for a Fermi liquid, but anomalously slowly compared to the fully screened case. We obtain the asymptotic forms for the phase shifts for elastic scattering of the quasiparticles in the high-spin and low-spin channels.