4,101 research outputs found
Single or multi-flavor Kondo effect in graphene
Based on the tight-binding formalism, we investigate the Anderson and the
Kondo model for an adaom magnetic impurity above graphene. Different impurity
positions are analyzed. Employing a partial wave representation we study the
nature of the coupling between the impurity and the conducting electrons. The
components from the two Dirac points are mixed while interacting with the
impurity. Two configurations are considered explicitly: the adatom is above one
atom (ADA), the other case is the adatom above the center the honeycomb (ADC).
For ADA the impurity is coupled with one flavor for both A and B sublattice and
both Dirac points. For ADC the impurity couples with multi-flavor states for a
spinor state of the impurity. We show, explicitly for a 3d magnetic atom,
, (,), and (,) couple
respectively with the , , and representations (reps) of group in ADC case. The basses for
these reps of graphene are also derived explicitly. For ADA we calculate the
Kondo temperature.Comment: 11 pages, 1 fures, 2 tables, accepted by EP
Laser-assisted spin-polarized transport in graphene tunnel junctions
Keldysh nonequilibrium Green's function method is utilized to study
theoretically the spin polarized transport through a graphene spin valve
irradiated by a monochromatic laser field. It is found that the bias dependence
of the differential conductance exhibits successive peaks corresponding to the
resonant tunneling through the photon-assisted sidebands. The multi photon
processes originate from the combined effects of the radiation field and the
graphene tunneling properties, and are shown to be substantially suppressed in
a graphene spin valve which results in a decrease of the differential
conductance for a high bias voltage. We also discussed the appearance of a
dynamical gap around zero bias due to the radiation field. The gap width can be
tuned by changing the radiation electric field strength and the frequency. This
leads to a shift of the resonant peaks in the differential conductance. We also
demonstrate numerically the dependencies of the radiation and spin valve
effects on the parameters of the external fields and those of the electrodes.
We find that the combined effects of the radiation field, the graphene, and the
spin valve properties bring about an oscillatory behavior in the tunnel
magnetoresistance (TMR), and this oscillatory amplitude can be changed by
scanning the radiation field strength and/or the frequency.Comment: 31 pages, 5 figures, corrected version to the paper in J. Phys.:
Condens. Matter 24 (2012) 26600
Magneto-transport in impurity-doped few-layer graphene spin valve
Using Keldysh nonequilibrium Green's function method we study the
spin-dependent transport through impurity-doped few layer graphene sandwiched
between two magnetic leads with an arbitrary mutual orientations of the
magnetizations. We find for parallel electrodes magnetizations that the
differential conductance possesses two resonant peaks as the applied bias
increases. These peaks are traced back to a buildup of a magnetic moment on the
impurity due to the electrodes spin polarization. For a large mutual angle of
the electrodes magnetization directions, the two resonant peaks approach each
others and merge into a single peak for antiparallel orientation of the
electrodes magnetizations. We point out that the tunneling magnetoresistance
(TMR) may change sign for relatively small changes in the values of the
polarization parameters. Furthermore, we inspect the behaviour of the
differential conductance and TMR upon varying the temperature.Comment: 8 pages, 7 figures, accepted by Phys. Rev.
Imprints of Schwinger Effect on Primordial Spectra
We study the Schwinger effect during inflation and its imprints on the
primordial power spectrum and bispectrum. The produced charged particles by
Schwinger effect during inflation can leave a unique angular dependence on the
primordial spectra.Comment: 27 pages, 13 figures, JHEP accepted versio
TCTAP A-172 Association Between Serum Uric Acid and eGFR in Patients with Type 2 Diabetes and Coronary Artery Disease
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