7,376 research outputs found

    Josephson junction on one edge of a two dimensional topological insulator affected by magnetic impurity

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    Current-phase relation in a Josephson junction formed by putting two s-wave superconductors on the same edge of a two dimensional topological insulator is investigated. We consider the case that the junction length is finite and magnetic impurity exists. The similarity and difference with conventional Josephson junction is discussed. The current is calculated in the semiconductor picture. Both the 2π2\pi- and 4π4\pi-period current-phase relations (I2π(ϕ),I4π(ϕ)I_{2\pi}(\phi), I_{4\pi}(\phi)) are studied. There is a sharp jump at ϕ=π\phi=\pi and ϕ=2π\phi=2\pi for I2πI_{2\pi} and I4πI_{4\pi} respectively in the clean junction. For I2πI_{2\pi}, the sharp jump is robust against impurity strength and distribution. However for I4πI_{4\pi}, the impurity makes the jump at ϕ=2π\phi=2\pi smooth. The critical (maximum) current of I2πI_{2\pi} is given and we find it will be increased by asymmetrical distribution of impurity.Comment: 7 pages, 5 figure

    Thermal entanglement in a two-spin-qutrit system under a nonuniform external magnetic field

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    The thermal entanglement in a two-spin-qutrit system with two spins coupled by exchange interaction under a magnetic field in an arbitrary direction is investigated. Negativity, the measurement of entanglement, is calculated. We find that for any temperature the evolvement of negativity is symmetric with respect to magnetic field. The behavior of negativity is presented for four different cases. The results show that for different temperature, different magnetic field give maximum entanglement. Both the parallel and antiparallel magnetic field cases are investigated qualitatively (not quantitatively) in detail, we find that the entanglement may be enhanced under an antiparallel magnetic field.Comment: 2 eps figure

    Bipolaronic blockade effect in quantum dots with negative charging energy

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    We investigate single-electron transport through quantum dots with negative charging energy induced by a polaronic energy shift. For weak dot-lead tunnel couplings, we demonstrate a bipolaronic blockade effect at low biases which suppresses the oscillating linear conductance, while the conductance resonances under large biases are enhanced. Novel conductance plateau develops when the coupling asymmetry is introduced, with its height and width tuned by the coupling strength and external magnetic field. It is further shown that the amplitude ratio of magnetic-split conductance peaks changes from 3 to 1for increasing coupling asymmetry. Though we demonstrate all these transport phenomena in the low-order single-electron tunneling regime, they are already strikingly different from the usual Coulomb blockade physics and are easy to observe experimentally.Comment: 6 pages, 5 figure

    Thermal entanglement in a two-qubit Heisenberg XXZ spin chain under an inhomogeneous magnetic field

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    The thermal entanglement in a two-qubit Heisenberg \emph{XXZ} spin chain is investigated under an inhomogeneous magnetic field \emph{b}. We show that the ground-state entanglement is independent of the interaction of \emph{z}-component JzJ_{z}. The thermal entanglement at the fixed temperature can be enhanced when JzJ_{z} increases. We strictly show that for any temperature \emph{T} and JzJ_{z} the entanglement is symmetric with respect to zero inhomogeneous magnetic field, and the critical inhomogeneous magnetic field bcb_{c} is independent of JzJ_{z}. The critical magnetic field BcB_{c} increases with the increasing b|b| but the maximum entanglement value that the system can arrive becomes smaller.Comment: 5 EPS figure

    Transition magnetic moment of Majorana neutrinos in the μν\mu\nuSSM

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    The nonzero vacuum expectative values of sneutrinos induce spontaneously R-parity and lepton number violation, and generate three tiny Majorana neutrino masses through the seesaw mechanism in the μν\mu\nuSSM, which is one of Supersymmetric extensions beyond Standard Model. Applying effective Lagrangian method, we study the transition magnetic moment of Majorana neutrinos in the model here. Under the constraints from neutrino oscillations, we consider the two possibilities on the neutrino mass spectrum with normal or inverted ordering.Comment: 20 pages, 2 figures, accepted for publication in JHEP. arXiv admin note: text overlap with arXiv:1305.4352, arXiv:1304.624
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