New Journal of Physics Phase lapses in transmission through interacting two-level quantum dots

doi:10.1088/1367-2630/9/5/123 Abstract. We investigate the appearance of π lapses in the transmission phase θ of a two-level quantum dot with Coulomb interaction U. Using the numerical and functional renormalization groupmethodswe study the entire parameter space for spin-polarized as well as spin-degenerate dots, modelled by spinless or spinful electrons, respectively. We investigate the effect of finite temperatures T. For small T and sufficiently small single-particle spacings δ of the dot levels we find π phase lapses between two transmission peaks in an overwhelming part of the parameter space of the level-lead couplings. For large δ the appearance or not of a phase lapse between resonances depends on the relative sign of the level-lead couplings in analogy to the U = 0 case. We show that this generic scenario is the same for spin-polarized and spin-degenerate dots. We emphasize that in contrast to dots with more levels, for a two-level dot with small δ and generic dot-lead couplings (that is up to cases with special symmetry) the ‘universal ’ phase lapse behaviour is already established at U = 0. The most important effect of th