7,376 research outputs found

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

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 $2\pi$- and $4\pi$-period current-phase relations
($I_{2\pi}(\phi), I_{4\pi}(\phi)$) are studied. There is a sharp jump at
$\phi=\pi$ and $\phi=2\pi$ for $I_{2\pi}$ and $I_{4\pi}$ respectively in the
clean junction. For $I_{2\pi}$, the sharp jump is robust against impurity
strength and distribution. However for $I_{4\pi}$, the impurity makes the jump
at $\phi=2\pi$ smooth. The critical (maximum) current of $I_{2\pi}$ 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

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

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

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 $J_{z}$. The thermal entanglement at the fixed temperature
can be enhanced when $J_{z}$ increases. We strictly show that for any
temperature \emph{T} and $J_{z}$ the entanglement is symmetric with respect to
zero inhomogeneous magnetic field, and the critical inhomogeneous magnetic
field $b_{c}$ is independent of $J_{z}$. The critical magnetic field $B_{c}$
increases with the increasing $|b|$ but the maximum entanglement value that the
system can arrive becomes smaller.Comment: 5 EPS figure

### Transition magnetic moment of Majorana neutrinos in the $\mu\nu$SSM

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 $\mu\nu$SSM, 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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