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Authors: Enrique Muñoz, Carlos J. Bolech (University of Cincinnati) and Stefan Kirchner (MPIPKS Dresden) We study nonequilibrium electronic transport through a quantum dot coupled to metallic leads at low but finite bias voltage V, and low temperature T. We model the system by an Anderson impurity Hamiltonian, and consider the electron-hole non-symmetric case, with the parameter Ed = E0+U/2 characterizing the extent of asymmetry. By extending the super-perturbation technique developed by Hafermann et al. (EPL 85 (2009), 27007) to the non-equilibrium case, we propose a fieldtheoretical perturbative scheme in the Keldysh contour, in order to study the effect of electron-hole asymmetry in the quasi-particle Green's function matrix in the Schwinger-Keldysh representation. By obtaining explicit analytical expressions for the Green's function and self-energy components at low T, V and frequency, for the weakly asymmetric (Ed ≠ 0) and interacting limit (U ≠ 0), we show that the proposed perturbative method provides a current conserving approximation. Moreover, we obtain an explicit analytical expression for the differential conductance dI/dV through the quantum dot up to quadratic order in T, V , U and electron-hole asymmetry parameter Ed. In particular, in the limit Ed → 0, our analytical expression for the conductance reduces to the formula reported by Rincón et al. (Phys. Rev. B 79 (2009), 121301(R)). |
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