title: Gate-controlled transitions in triple dots with interdot repulsion and magnetic field.
abstract: We study the quantum phase transition (QPT) and electronic transport in triple quantum dots for a wide range of the gate voltage ϵ. We focus on the effect of the interdot repulsion V and the magnetic field B. In the case of particle-hole (p-h) symmetry and B = 0, we find the local quadruplet-doublet transition of first order when V increases to a critical point V(c) ≈ U, where U is the on-site repulsion. Beyond the p-h symmetry, the sequence of the QPTs depends on ϵ. For small ϵ, a first order doublet-singlet transition is observed. For middle ϵ, we find the quadruplet-triplet transition of first order at V(c1) and the triplet-singlet transition of the Kosterlitz-Thouless type at V(c2). For large ϵ, there are two kinds of first order QPT with phase sequence quadruplet-triplet-doublet. The magnetic field B compensates for the effect of V. For V > U, as B increases we find a first order or second order QPT from a low-spin state to a high-spin state. The restoring of the Kondo effect and a perfect spin filtering is realized in the appropriate regime of the magnetic field.
authors.affiliation: Department of Physics, Wuhan University, and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Wuhan 430072, People's Republic of China.
authors.forename: Yong-Chen
authors.initials: YC
authors.lastname: Xiong
authors.forename: Jin
authors.initials: J
authors.lastname: Huang
authors.forename: Wei-Zhong
authors.initials: WZ
authors.lastname: Wang