title: Quantum phase transition and emergent symmetry in a quadruple quantum dot system.
abstract: We propose a system of four quantum dots designed to study the competition between three types of interactions: Heisenberg, Kondo, and Ising. We find a rich phase diagram containing two sharp features: a quantum phase transition (QPT) between charge-ordered and charge-liquid phases and a dramatic resonance in the charge liquid visible in the conductance. The QPT is of the Kosterlitz-Thouless type with a discontinuous jump in the conductance at the transition. We connect the resonance phenomenon with the degeneracy of three levels in the isolated quadruple dot and argue that this leads to a Kondo-like emergent symmetry from left-right Z2 to U(1).
authors.affiliation: Department of Physics, Duke University, Box 90305, Durham, North Carolina 27708-0305, USA.
authors.forename: Dong E
authors.initials: DE
authors.lastname: Liu
authors.forename: Shailesh
authors.initials: S
authors.lastname: Chandrasekharan
authors.forename: Harold U
authors.initials: HU
authors.lastname: Baranger