Effects of orbital splitting on the three-body Fermi liquid corrections for an infinite-U Anderson impurity

We investigate the influence of orbital splitting on the low-energy Fermi-liquid properties and nonlinear transport through the N-level Anderson impurity model in the strong-interaction limit U → ∞. Specifically, we focus on the N = 4 case, which is relevant to carbon nanotube quantum dots, and consider an orbital-splitting field that breaks the SU(4) symmetry down to SU(2)×SU(2). In this limit, the impurity occupation number N_d varies in the range 0 ≤ N_d ≤ 1, and the SU(4) Kondo effect occurs near N_d = 1 in the absence of orbital splitting, continuously evolving into an SU(2) Kondo state as the splitting increases. Using the latest version of the Fermi-liquid theory together with the numerical renormalization group (NRG) approach, we show how the three-body correlations between impurity electrons affect the next-to-leading-order terms of the differential conductance and current noise. Our analysis also provides a way to deduce the three-body correlations from measurements of the next-to-leading-order terms of the transport coefficients.