Role of bias and tunneling asymmetries in nonlinear Fermi-liquid transport through an SU(N) quantum dot

We study the effects of bias and tunneling asymmetries on the nonlinear current through a quantum dot with N discrete levels in the Fermi liquid regime, using an exact low-energy expansion based on the Anderson impurity model [1]. The expansion coefficients, obtained up to terms of order V³ in powers of the bias voltage, are described in terms of the phase shift, the linear susceptibilities, and the three-body correlation functions, defined with respect to the equilibrium ground state. When the system does not have the electron-hole and the time-reversal symmetries, the three-body correlations play an essential role in the order V³ nonlinear current that depends significantly on the bias and tunnel asymmetries. We calculate the expansion coefficients for SU(N) symmetric quantum dots with N=4 and N=6, using the numerical renormalization group across a wide range of electron fillings, and clarify the contribution of three-body Fermi-liquid effects emerging in the Kondo states at electron-hole asymmetric integer-filling points and in the valence fluctuation region. [1] K. Tsutsumi, Y. Teratani, K. Motoyama, R. Sakano, and A. Oguri, PRB 108, 045109 (2023).