Perturbation study of the conductance through a finite Hubbard chain

Transport through a Hubbard chain of size N (=1,2,3,...) connected to reservoirs is studied at T = 0 in an electron-hole symmetric case based on the second-order perturbation theory in U. The result shows a typical even-odd property corresponding to a Kondo or Mott-Hubbard physics. In this report, specifically, we study the dependence of the conductance on the coupling between the chain and reservoirs, which was not examined in detail in our previous report [Phy. Rev. B 59, 12240 (1999)].Comment: 2 pages, LaTeX, submitted to LT22 (Physica B

Transmission probability through small interacting systems: application to a series of quantum dots

We apply a theory for the transmission probability of small interacting systems, which was formulated based on the Kubo formalism in our previous study, to a series of quantum dots described by the N-impurity Anderson model. In this report, we present the transmission pobability for the system of N=2 calculated using the order $U^2$ self-energy and vertex corrections. Particularly, we examine the features in the two typical parameter regions, $t\Gamma$, where the Kondo effect or the inter-dot correlation dominates. Here, $t$ is the inter-dot transfer and $\Gamma$ is the level broadening caused by the coupling with the noninteracting leads.Comment: 2 pages, 2 figures: proccedings of LT23 (Hiroshima, August, 2002

Kondo screening of a high-spin Nagaoka state in a triangular quantum dot

We study transport through a triangle triple quantum dot connected to two noninteracting leads using the numerical renormalization group (NRG). The triangle has a high-spin ground state of S=1 caused by a Nagaoka ferromagnetism, when it is isolated and has one extra electron introduced into a half-filling. The results show that the conduction electrons screen the local moment via two separate stages with different energy scales. The half of the S=1 is screened first by one of the channel degrees, and then at very low temperature the remaining half is fully screened to form a Kondo singlet. The transport is determined by two phase shifts for quasi-particles with even and odd parities, and then a two-terminal conductance in the series configuration is suppressed $g_{\rm series} \simeq 0$, while plateau of a four-terminal parallel conductance reaches a Unitary limit value $g_{\rm parallel} \simeq 4e^2/h$ of two conducting modes.Comment: 2pages, 2figures: fig1 is revised to show a narrow dip found in the series conductanc