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We study the nonlinear conductance through a quantum dot, specifically itsdependence on the asymmetries in the tunnel couplings and bias voltages $V$, atlow energies. Extending the microscopic Fermi-liquid theory for the Andersonimpurity model, we obtain an exact formula for the steady current $I$ up toterms of order $V^3$ in the presence of these asymmetries. The coefficients forthe nonlinear terms are described in terms of a set of the Fermi-liquidparameters: the phase shift, static susceptibilities, and three-bodycorrelation functions of electrons in the quantum dots, defined with respect tothe equilibrium ground state. We calculate these correlation functions, usingthe numerical renormalization group approach (NRG), over a wide range ofimpurity-electron filling that can be controlled by a gate voltage in realsystems. The NRG results show that the order $V^2$ nonlinear current isenhanced significantly in the valence fluctuation regime. It is caused by theorder $V$ energy shift of the impurity level, induced in the presence of thetunneling or bias asymmetry. Furthermore, in the valence fluctuation regime, wealso find that the order $V^3$ nonlinear current exhibits a shoulder structure,for which the three-body correlations that evolve for large asymmetries play anessential role.

Nonlinear Fermi-liquid transport through a quantum dot in asymmetric tunnel junctions