554 research outputs found
Quantum discord in spin-cluster materials
The total quantum correlation (discord) in Heisenberg dimers is expressed via
the spin-spin correlation function, internal energy, specific heat or magnetic
susceptibility. This allows one to indirectly measure the discord through
neutron scattering, as well as calorimetric or magnetometric experiments. Using
the available experimental data, we found the discord for a number of binuclear
Heisenberg substances with both antiferro- and ferromagnetic interactions. For
the dimerized antiferromagnet copper nitrate Cu(NO_3)_2*2.5H_2O, the three
independent experimental methods named above lead to a discord of approximately
0.2-0.3 bit/dimer at a temperature of 4 K. We also determined the temperature
behavior of discord for hydrated and anhydrous copper acetates, as well as for
the ferromagnetic binuclear copper acetate complex [Cu_2L(OAc)]*6H_2O, where L
is a ligand.Comment: 7 pages, 6 figure
On Multiparticle Entanglement via Resonant Interaction between Light and atomic Ensembles
Multiparticle entangled states generated via interaction between narrow-band
light and an ensemble of identical two-level atoms are considered. Depending on
the initial photon statistics, correlation between atoms and photons can give
rise to entangled states of these systems. It is found that the state of any
pair of atoms interacting with weak single-mode squeezed light is inseparable
and robust against decay. Optical schemes for preparing entangled states of
atomic ensembles by projective measurement are described.Comment: 11 pages, 1 figure, revtex
Stacking boundaries and transport in bilayer graphene
Pristine bilayer graphene behaves in some instances as an insulator with a
transport gap of a few meV. This behaviour has been interpreted as the result
of an intrinsic electronic instability induced by many-body correlations.
Intriguingly, however, some samples of similar mobility exhibit good metallic
properties, with a minimal conductivity of the order of . Here we
propose an explanation for this dichotomy, which is unrelated to electron
interactions and based instead on the reversible formation of boundaries
between stacking domains (`solitons'). We argue, using a numerical analysis,
that the hallmark features of the previously inferred many-body insulating
state can be explained by scattering on boundaries between domains with
different stacking order (AB and BA). We furthermore present experimental
evidence, reinforcing our interpretation, of reversible switching between a
metallic and an insulating regime in suspended bilayers when subjected to
thermal cycling or high current annealing.Comment: 13 pages, 15 figures. Published version (Nano Letters
Conductance of p-n-p graphene structures with 'air-bridge' top gates
We have fabricated graphene devices with a top gate separated from the
graphene layer by an air gap--a design which does not decrease the mobility of
charge carriers under the gate. This gate is used to realise p-n-p structures
where the conducting properties of chiral carriers are studied. The band
profile of the structures is calculated taking into account the specifics of
the graphene density of states and is used to find the resistance of the p-n
junctions expected for chiral carriers. We show that ballistic p-n junctions
have larger resistance than diffusive ones. This is caused by suppressed
transmission of chiral carriers at angles away from the normal to the junction.Comment: to be published in Nano Letter
Giant Spin-Hall Effect induced by Zeeman Interaction in Graphene
We propose a new approach to generate and detect spin currents in graphene,
based on a large spin-Hall response arising near the neutrality point in the
presence of external magnetic field. Spin currents result from the imbalance of
the Hall resistivity for the spin-up and spin-down carriers induced by Zeeman
interaction, and do not involve spin-orbit interaction. Large values of the
spin-Hall response achievable in moderate magnetic fields produced by on-chip
sources, and up to room temperature, make the effect viable for spintronics
applications
Quantum transport thermometry for electrons in graphene
We propose a method of measuring the electron temperature in mesoscopic
conductors and demonstrate experimentally its applicability to micron-size
graphene devices in the linear-response regime (, the bath
temperature). The method can be {especially useful} in case of overheating,
. It is based on analysis of the correlation function of mesoscopic
conductance fluctuations. Although the fluctuation amplitude strongly depends
on the details of electron scattering in graphene, we show that extracted
from the correlation function is insensitive to these details.Comment: 4 pages, 4 figures; final version, as publishe
On the Mass Eigenstate Composition of the 8B Neutrinos from the Sun
The present data of gallium experiments provide indirectly the only
experimental limit on the fraction of mass eigenstate for the B
neutrinos from the Sun. However, if to use the experimental data alone, the
fraction of and, consequently, still is allowed to
be varied within a rather broad range. The further experimental efforts are
needed to clear this point.Comment: 13 pages, 1 figure, 1 table. Corrected version, published in
JCAP04(2007)00
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