13 research outputs found
Quantum nonlinear planar Hall effect in bilayer graphene: an orbital effect of a steady in-plane magnetic field
We study the quantum nonlinear planar Hall effect in bilayer graphene under a
steady in-plane magnetic field. When time-reversal symmetry is broken by the
magnetic field, a charge current occurs in the second-order response to an
external electric field, as a result of the Berry curvature dipole in momentum
space. We have shown that a nonlinear planar Hall effect originating from the
anomalous velocity is deduced by an orbital effect of an in-plane magnetic
field on electrons in bilayer graphene in the complete absence of spin-orbit
coupling. Taking into account the symmetry analysis, we derived the dominant
dependence of Berry curvature dipole moment on the magnetic field components.
Moreover, we illustrate how to control and modulate the Berry curvature dipole
with an external planar magnetic field, gate voltage, and Fermi energy
Thermal conductivity of anisotropic spin - 1/2 two leg ladder:Green's function approach
We study the thermal transport of a spin-1/2 two leg antiferromagnetic ladder
in the direction of legs. The possible effect of spin-orbit coupling and
crystalline electric field are investigated in terms of anisotropies in the
Heisenberg interactions on both leg and rung couplings. The original spin
ladder is mapped to a bosonic model via a bond-operator transformation where an
infinite hard-core repulsion is imposed to constrain one boson occupation per
site. The Green's function approach is applied to obtain the energy spectrum of
quasi-particle excitations responsible for thermal transport. The thermal
conductivity is found to be monotonically decreasing with temperature due to
increased scattering among triplet excitations at higher temperatures. A tiny
dependence of thermal transport on the anisotropy in the leg direction at low
temperatures is observed in contrast to the strong one on the anisotropy along
the rung direction, due to the direct effect of the triplet density. Our
results reach asymptotically the ballistic regime of the spin - 1/2 Heisenberg
chain and compare favorably well with exact diagonalization data
Unusual magnetic phases in the strong interaction limit of two-dimensional topological band insulators in transition metal oxides
The expected phenomenology of non-interacting topological band insulators
(TBI) is now largely theoretically understood. However, the fate of TBIs in the
presence of interactions remains an active area of research with novel,
interaction-driven topological states possible, as well as new exotic magnetic
states. In this work we study the magnetic phases of an exchange Hamiltonian
arising in the strong interaction limit of a Hubbard model on the honeycomb
lattice whose non-interacting limit is a two-dimensional TBI recently proposed
for the layered heavy transition metal oxide compound, (Li,Na)IrO. By a
combination of analytical methods and exact diagonalization studies on finite
size clusters, we map out the magnetic phase diagram of the model. We find that
strong spin-orbit coupling can lead to a phase transition from an
antiferromagnetic Ne\'el state to a spiral or stripy ordered state. We also
discuss the conditions under which a quantum spin liquid may appear in our
model, and we compare our results with the different but related
Kitaev-Heisenberg-- model which has recently been studied in a
similar context.Comment: 12 pages, 8 figure
A Model to Publish Online Social Networks Data with Privacy Preserving
Nowadays the growth in the use of social networks among different classes of world community is increasingly undeniable. Social networks database include Rich and valuable resources whose release and analysis with the purpose of marketing, publicity, National Security, Health and etc. can benefit researchers of public and private institutions. But respect the privacy of the entities whose information is available to data miner analysis is essential as a legal protocol. In this Paper, through qualitative methodology Meta synthesis, all related dimensions, indicators and codes were identified and then the importance and priority of each of the factors was determined. Subsequently, the improved model of anonymity was presented by an optimizing firefly algorithm and fuzzy clustering. The result of simulation and assessment of the proposed model on the data of four social networks such as Facebook, YouTube, Twitter and Google+ depicts that privacy preserving of data with the lowest distortion ratio and the more usefulness of data