Electronic transport through a quantum dot with metallic contacts

We present a microscopic Green's function theory of electrical transport through a quantum dot with metallic contacts. The quantum dot has a single degenerate level where the energy level is split by a structural distortion (Jahn-Teller distortion). The calculation includes the effect of Coulomb blockade as well as the effect of presence of a magnetic impurity. The two metallic leads are represented by the free electron gas model and their interaction with the dot levels provides their width. The J-T distortion order parameter and the occupancy of the dot levels by up and down spin electrons are calculated self consistently as a function of temperature. These results are used to calculate the electrical conductivity as a function of the temperature. It is found that the J-T distortion order parameter depends strongly on the location of the dot energy level with respect to the Fermi level. While this order parameter shows a first order transition (discontinuous drop to zero) in the absence of the width of the dot level, it shows a second order transition and a reentrant behavior (for low dot energy levels) in its presence. The electrical conductivity has strong dependence on temperature, dot energy, its width, J-T distortion parameter, and magnetization due to the magnetic impurity.