The Finite-UU Impurity Anderson Model in the presence of an external magnetic field

We have investigated effects of an external magnetic field in the impurity Anderson model with a finite on-site Coulomb repulsion $U$. Large $N_f$ expansion is employed in the slave boson representation, by taking into account $f^0$, $f^1$, and $f^2$ subspaces. To evaluate the vertex function for the ``empty state boson" self-energy, we have devised two approximations which reduce much computational efforts without losing general features of the model. It is found that the Kondo temperature is reduced by the presence of a magnetic field, and that at low field and at low temperature, the field dependence of both the Kondo temperature and the impurity magnetization exhibits a scaling behavior with high accuracy. Further, some interesting features are found in the field dependence of the impurity magnetization at finite temperature, the physical implications of which are discussed in terms of the renormalized Kondo temperature.Comment: 18 pages Revtex, 7 Postscript figures, To appear in Phys.Rev.

On the validity and breakdown of the Onsager symmetry in mesoscopic conductors interacting with environments

We investigate magnetic-field asymmetries in the linear transport of a mesoscopic conductor interacting with its environment. Interestingly, we find that the interaction between the two systems causes an asymmetry only when the environment is out of equilibrium. We elucidate our general result with the help of a quantum dot capacitively coupled to a quantum Hall conductor and discuss the asymmetry dependence on the environment bias and induced dephasing.Comment: 4 pages, 4 figures; discussions clarified; published versio