2,566 research outputs found
Hadronic current correlation functions at finite temperature in the NJL model
Recently there have been suggestions that for a proper description of
hadronic matter and hadronic correlation functions within the NJL model at
finite density/temperature the parameters of the model should be taken
density/temperature dependent. Here we show that qualitatively similar results
can be obtained using a cutoff-independent regularization of the NJL model. In
this regularization scheme one can express the divergent parts at finite
density/temperature of the amplitudes in terms of their counterparts in vacuum.Comment: Presented at 9th Hadron Physics and 8th Relativistic Aspects of
Nuclear Physics (HADRON-RANP 2004): A Joint Meeting on QCD and QGP, Angra dos
Reis, Rio de Janeiro, Brazil, 28 Mar - 3 Apr 200
Cutoff-independent regularization of four-fermion interactions for color superconductivity
We implement a cutoff-independent regularization of four-fermion interactions
to calculate the color-superconducting gap parameter in quark matter. The
traditional cutoff regularization has difficulties for chemical potentials \mu
of the order of the cutoff \Lambda, predicting in particular a vanishing gap at
\mu \sim \Lambda. The proposed cutoff-independent regularization predicts a
finite gap at high densities and indicates a smooth matching with the weak
coupling QCD prediction for the gap at asymptotically high densities.Comment: 5 pages, 1 eps figure - Revised manuscript to match the published
pape
Wave packet dynamics and valley filter in strained graphene
The time evolution of a wavepacket in strained graphene is studied within the
tight-binding model and continuum model. The effect of an external magnetic
field, as well as a strain-induced pseudo-magnetic field, on the wave packet
trajectories and zitterbewegung are analyzed. Combining the effects of strain
with those of an external magnetic field produces an effective magnetic field
which is large in one of the Dirac cones, but can be practically zero in the
other. We construct an efficient valley filter, where for a propagating
incoming wave packet consisting of momenta around the K and K' Dirac points,
the outgoing wave packet exhibits momenta in only one of these Dirac points,
while the components of the packet that belong to the other Dirac point are
reflected due to the Lorentz force. We also found that the zitterbewegung is
permanent in time in the presence of either external or strain-induced magnetic
fields, but when both the external and strain-induced magnetic fields are
present, the zitterbewegung is transient in one of the Dirac cones, whereas in
the other cone the wave packet exhibits permanent spatial oscillations.Comment: 13 pages, 10 figure
Extension of the Nambu--Jona-Lasinio model at high densities and temperatures by using an implicit regularization scheme
Traditional cutoff regularization schemes of the Nambu--Jona-Lasinio model
limit the applicability of the model to energy-momentum scales much below the
value of the regularizing cutoff. In particular, the model cannot be used to
study quark matter with Fermi momenta larger than the cutoff. In the present
work an extension of the model to high temperatures and densities recently
proposed by Casalbuoni, Gatto, Nardulli, and Ruggieri is used in connection
with an implicit regularization scheme. This is done by making use of scaling
relations of the divergent one-loop integrals that relate these integrals at
different energy-momentum scales. Fixing the pion decay constant at the chiral
symmetry breaking scale in the vacuum, the scaling relations predict a running
coupling constant that decreases as the regularization scale increases,
implementing in a schematic way the property of asymptotic freedom of quantum
chromodynamics. If the regularization scale is allowed to increase with density
and temperature, the coupling will decrease with density and temperature,
extending in this way the applicability of the model to high densities and
temperatures. These results are obtained without specifying an explicit
regularization. As an illustration of the formalism, numerical results are
obtained for the finite density and finite temperature quark condensate, and to
the problem of color superconductivity at high quark densities and finite
temperature.Comment: 7 pages, 5 eps figures - in version 3, substantial changes in text,
results and conclusions unchanged. To be published in Phys. Rev.
Wavepacket scattering on graphene edges in the presence of a (pseudo) magnetic field
The scattering of a Gaussian wavepacket in armchair and zigzag graphene edges
is theoretically investigated by numerically solving the time dependent
Schr\"odinger equation for the tight-binding model Hamiltonian. Our theory
allows to investigate scattering in reciprocal space, and depending on the type
of graphene edge we observe scattering within the same valley, or between
different valleys. In the presence of an external magnetic field, the well know
skipping orbits are observed. However, our results demonstrate that in the case
of a pseudo-magnetic field, induced by non-uniform strain, the scattering by an
armchair edge results in a non-propagating edge state.Comment: 8 pages, 7 figure
All-strain based valley filter in graphene nanoribbons using snake states
A pseudo-magnetic field kink can be realized along a graphene nanoribbon
using strain engineering. Electron transport along this kink is governed by
snake states that are characterized by a single propagation direction. Those
pseudo-magnetic fields point towards opposite directions in the K and K'
valleys, leading to valley polarized snake states. In a graphene nanoribbon
with armchair edges this effect results in a valley filter that is based only
on strain engineering. We discuss how to maximize this valley filtering by
adjusting the parameters that define the stress distribution along the graphene
ribbon.Comment: 8 pages, 6 figure
Topological confinement in graphene bilayer quantum rings
We demonstrate the existence of localized electron and hole states in a
ring-shaped potential kink in biased bilayer graphene. Within the continuum
description, we show that for sharp potential steps the Dirac equation
describing carrier states close to the K (or K') point of the first Brillouin
zone can be solved analytically for a circular kink/anti-kink dot. The
solutions exhibit interfacial states which exhibit Aharonov-Bohm oscillations
as functions of the height of the potential step and/or the radius of the ring
Conditions for non-monotonic vortex interaction in two-band superconductors
We describe a semi-analytic approach to the two-band Ginzburg-Landau theory,
which predicts the behavior of vortices in two-band superconductors. We show
that the character of the short-range vortex-vortex interaction is determined
by the sign of the normal domain - superconductor interface energy, in analogy
with the conventional differentiation between type-I and type-II
superconductors. However, we also show that the long-range interaction is
determined by a modified Ginzburg-Landau parameter , different from
the standard of a bulk superconductor. This opens the possibility for
non-monotonic vortex-vortex interaction, which is temperature-dependent, and
can be further tuned by alterations of the material on the microscopic scale
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