Strong vs. Weak Coupling Duality and Coupling Dependence of the Kondo Temperature in the Two-Channel Kondo Model

We perform numerical renormalization group (NRG) as well as analytical calculations for the two-channel Kondo model to obtain the dependence of the Kondo temperature $T_K$ on the dimensionless (bare) spin exchange coupling $g$ over the complete parameter range from $g\ll 1$ to $g\gg 1$. We show that there exists a duality between the regimes of small and large coupling. It is unique for the two-channel model and enables a mapping between the strong and the weak coupling cases via the identification $g\leftrightarrow 3/(2g)$, implying an exponential dependence of $T_K$ on $1/g$ and $g$, respectively, in the two regimes. This agrees quantitatively with our NRG calculations where we extract $T_K(g)$ over the complete parameter range and obtain a non-monotonous $T_K(g)$ dependence, strongly peaked at the 2CK fixed point coupling $g^*$. These results may be relevant for resolving the long-standing puzzle within the 2CK interpretation of certain random defect systems, why no broad distribution of $T_K$ is observed in those systems.Comment: 6 pages, 3 figures; PRB published version, shortened, nomenclature clarifie

Spurrekonstruktion in der Hexagonal-Driftkammer am Experiment COSY-11

The experimental facility COSY-11 at the cooler synchrotron and storage ring COSY at the Research Center Jülich investigates the production of Small width mesons in the proton-proton- and proton-deuteron-interaction close to threshold . At COSY-11, the trajectories of positively charged ejectiles are measured by means of two planar drift chamber systems . In summer 2000, a drift chamber wich hexagonal cells was added to the COSY-11 setup. Consequently, the acceptance for short-living, positively charged mesons like pions and kaons is increased . The trajectories in the hexagonal chamber can be determined with the new track reconstruction Software in three dimensions . With the data of the COSY-11 beamtime in March 2001 a calibration was performed. The position resolution, determined as the Standard deviation of the experimental data, amounts to 450 /Im

Numerical renormalization group studies in complex quantum impurity systems

In this thesis we summarize several theoretical studies in the context of quantum impurity systems. We implement the numerical renormalization group (NRG) technique as a powerful method for the solution of the Kondo and the Anderson impurity model. The extension of the standard NRG, which deals with static properties and the calculation of thermodynamics, towards the calculation of dynamical properties is accurately described in our work. We study the distribution of the Kondo temperature TK versus the Kondo coupling strength J in the two-channel Kondo (2CK) model by means of an extended NRG program. We show that a wide distribution of the couplings J leads to a peaked distribution of TK. This gives an explanation of the zero-bias anomalies measured in quantum point contact experiments. Conductance measurements in scanning tunneling microscopy (STM) experiments of transition metal impurities on metal surfaces are analyzed in this thesis. By combining correlated electron techniques with density functional calculations we show that the transport occurs through the atomic multi-electron states, and we identify their signature in the STM lineshape. A careful analysis of the different relative strengths of the transmission channels allows to determine the spatial orientation of the atomic orbitals of Kondo atoms on a metal surface. Our interpretation is that the tunneling predominantly occurs into the local orbital, which sticks out most out of the metal surface