title: Ground state of the parallel double quantum dot system.
abstract: We resolve the controversy regarding the ground state of the parallel double quantum dot system near half filling. The numerical renormalization group predicts an underscreened Kondo state with residual spin-1/2 magnetic moment, ln2 residual impurity entropy, and unitary conductance, while the Bethe ansatz solution predicts a fully screened impurity, regular Fermi-liquid ground state, and zero conductance. We calculate the impurity entropy of the system as a function of the temperature using the hybridization-expansion continuous-time quantum Monte Carlo technique, which is a numerically exact stochastic method, and find excellent agreement with the numerical renormalization group results. We show that the origin of the unconventional behavior in this model is the odd-symmetry "dark state" on the dots.
authors.affiliation: Jožef Stefan Institute, Ljubljana, Slovenia.
authors.forename: Rok
authors.initials: R
authors.lastname: Zitko
authors.forename: Jernej
authors.initials: J
authors.lastname: Mravlje
authors.forename: Kristjan
authors.initials: K
authors.lastname: Haule