59,532 research outputs found
Relativistic Effects of Mixed Vector-Scalar-Pseudoscalar Potentials for Fermions in 1+1 Dimensions
The problem of fermions in the presence of a pseudoscalar plus a mixing of
vector and scalar potentials which have equal or opposite signs is
investigated. We explore all the possible signs of the potentials and discuss
their bound-state solutions for fermions and antifermions. The cases of mixed
vector and scalar P\"{o}schl-Teller-like and pseudoscalar kink-like potentials,
already analyzed in previous works, are obtained as particular cases
Unified Treatment of Mixed Vector-Scalar Screened Coulomb Potentials for Fermions
The problem of a fermion subject to a general mixing of vector and scalar
screened Coulomb potentials in a two-dimensional world is analyzed and
quantization conditions are found.Comment: 7 page
Bilayer graphene: gap tunability and edge properties
Bilayer graphene -- two coupled single graphene layers stacked as in graphite
-- provides the only known semiconductor with a gap that can be tuned
externally through electric field effect. Here we use a tight binding approach
to study how the gap changes with the applied electric field. Within a parallel
plate capacitor model and taking into account screening of the external field,
we describe real back gated and/or chemically doped bilayer devices. We show
that a gap between zero and midinfrared energies can be induced and externally
tuned in these devices, making bilayer graphene very appealing from the point
of view of applications. However, applications to nanotechnology require
careful treatment of the effect of sample boundaries. This being particularly
true in graphene, where the presence of edge states at zero energy -- the Fermi
level of the undoped system -- has been extensively reported. Here we show that
also bilayer graphene supports surface states localized at zigzag edges. The
presence of two layers, however, allows for a new type of edge state which
shows an enhanced penetration into the bulk and gives rise to band crossing
phenomenon inside the gap of the biased bilayer system.Comment: 8 pages, 3 fugures, Proceedings of the International Conference on
Theoretical Physics: Dubna-Nano200
Algebraic solution of a graphene layer in a transverse electric and perpendicular magnetic fields
We present an exact algebraic solution of a single graphene plane in
transverse electric and perpendicular magnetic fields. The method presented
gives both the eigen-values and the eigen-functions of the graphene plane. It
is shown that the eigen-states of the problem can be casted in terms of
coherent states, which appears in a natural way from the formalism.Comment: 11 pages, 5 figures, accepted for publication in Journal of Physics
Condensed Matte
Conductivity of suspended and non-suspended graphene at finite gate voltage
We compute the DC and the optical conductivity of graphene for finite values
of the chemical potential by taking into account the effect of disorder, due to
mid-gap states (unitary scatterers) and charged impurities, and the effect of
both optical and acoustic phonons. The disorder due to mid-gap states is
treated in the coherent potential approximation (CPA, a self-consistent
approach based on the Dyson equation), whereas that due to charged impurities
is also treated via the Dyson equation, with the self-energy computed using
second order perturbation theory. The effect of the phonons is also included
via the Dyson equation, with the self energy computed using first order
perturbation theory. The self-energy due to phonons is computed both using the
bare electronic Green's function and the full electronic Green's function,
although we show that the effect of disorder on the phonon-propagator is
negligible. Our results are in qualitative agreement with recent experiments.
Quantitative agreement could be obtained if one assumes water molelcules under
the graphene substrate. We also comment on the electron-hole asymmetry observed
in the DC conductivity of suspended graphene.Comment: 13 pages, 11 figure
Stationary states of fermions in a sign potential with a mixed vector-scalar coupling
The scattering of a fermion in the background of a sign potential is
considered with a general mixing of vector and scalar Lorentz structures with
the scalar coupling stronger than or equal to the vector coupling under the
Sturm-Liouville perspective. When the vector coupling and the scalar coupling
have different magnitudes, an isolated solution shows that the fermion under a
strong potential can be trapped in a highly localized region without
manifestation of Klein's paradox. It is also shown that the lonely bound-state
solution disappears asymptotically as one approaches the conditions for the
realization of spin and pseudospin symmetries.Comment: 4 figure
Scattering and bound states of fermions in a mixed vector-scalar smooth step potential
The scattering of a fermion in the background of a smooth step potential is
considered with a general mixing of vector and scalar Lorentz structures with
the scalar coupling stronger than or equal to the vector coupling.
Charge-conjugation and chiral-conjugation transformations are discussed and it
is shown that a finite set of intrinsically relativistic bound-state solutions
appears as poles of the transmission amplitude. It is also shown that those
bound solutions disappear asymptotically as one approaches the conditions for
the realization of the so-called spin and pseudospin symmetries in a
four-dimensional space-time.Comment: 5 figures. arXiv admin note: substantial text overlap with
arXiv:1310.847
- …