492 research outputs found
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
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
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
Singular-phase nanooptics: towards label-free single molecule detection
Non-trivial topology of phase is crucial for many important physics phenomena
such as, for example, the Aharonov-Bohm effect 1 and the Berry phase 2. Light
phase allows one to create "twisted" photons 3, 4 , vortex knots 5,
dislocations 6 which has led to an emerging field of singular optics relying on
abrupt phase changes 7. Here we demonstrate the feasibility of singular
visible-light nanooptics which exploits the benefits of both plasmonic field
enhancement and non-trivial topology of light phase. We show that properly
designed plasmonic nanomaterials exhibit topologically protected singular phase
behaviour which can be employed to radically improve sensitivity of detectors
based on plasmon resonances. By using reversible hydrogenation of graphene 8
and a streptavidin-biotin test 9, we demonstrate areal mass sensitivity at a
level of femto-grams per mm2 and detection of individual biomolecules,
respectively. Our proof-of-concept results offer a way towards simple and
scalable single-molecular label-free biosensing technologies.Comment: 19 pages, 4 figure
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
Transient events in the near-nuclear regions of AGNs and quasars as the sources of the proper motion imitations
We present a sample of SRG/eROSITA X-ray sources located in the eastern
Galactic hemisphere (0<l<180 deg), with significant proper motions according to
GAIA eDR3 measurements and whose extragalactic nature has been confirmed. The
catalog consists of 248 extragalactic sources with spectroscopically measured
redshifts. It includes all objects available in the Simbad database and matched
to the identified optical component within a radius of 0.5 arcsec.
Additionally, the catalog includes 18 sources with the spectral redshift
measurements based on observations at the Russian-Turkish 1.5-m telescope
RTT-150. The sources of the catalog are AGNs of various types (Sy1, Sy2,
LINER), quasars, radio galaxies, and star-forming galaxies. The imitation of
significant proper motions can be explained (previously known in astrometry as
the VIM effect) by the presence of transient events on the line of sight in the
field of view of AGN nuclei and quasars (within the GAIA resolution element).
Such astrophysical phenomena may be the supernovae outbursts, tidal destruction
events in AGNs with double nuclei, variability of large-mass supergiants, the
presence of O-B associations in field of view of variable brightness AGN, etc.
A model of flares with a fast rise and exponential decay profile allows to
describe the variable positional parameters of most similar sources observed in
GAIA. This cross-matching approach of the X-ray source catalogs of the
SRG/eROSITA observatory and the optical catalog of the GAIA observatory can be
used as an independent technique for detecting transient events in the
neighborhood of AGN core (on scales of several hundred parsecs in the picture
plane).Comment: 23 pages, 8 figures, 10 table
Efficient symmetric multiparty quantum state sharing of an arbitrary m-qubit state
We present a scheme for symmetric multiparty quantum state sharing of an
arbitrary -qubit state with Greenberger-Horne-Zeilinger states following
some ideas from the controlled teleportation [Phys. Rev. A \textbf{72}, 02338
(2005)]. The sender Alice performs Bell-state measurements on her
particles and the controllers need only to take some single-photon product
measurements on their photons independently, not Bell-state measurements, which
makes this scheme more convenient than the latter. Also it does not require the
parties to perform a controlled-NOT gate on the photons for reconstructing the
unknown -qubit state and it is an optimal one as its efficiency for qubits
approaches the maximal value.Comment: 6 pages, no figures; It simplifies the process for sharing an
arbitrary m-qubit state in Phys. Rev. A 72, 022338 (2005) (quant-ph/0501129
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