276 research outputs found
Transport Properties of Solitons
We calculate in this article the transport coefficients which characterize
the dynamics of solitons in quantum field theory using the methods of
dissipative quantum systems. We show how the damping and diffusion coefficients
of soliton-like excitations can be calculated using the integral functional
formalism. The model obtained in this article has new features which cannot be
obtained in the standard models of dissipation in quantum mechanics.Comment: 16 Pages, RevTeX, Preprint UIU
New Model For Dissipation In Quantum Mechanics
We propose a new model for studying dissipation in quantum-mechanical systems. The mechanism of dissipation is solely due to the scattering of the environment excitations by the particle of interest. We treat the problem via the functional integral formalism. It is shown that the model gives a damping parameter which is temperature dependent.67151960196
Strongly correlated fermions with nonlinear energy dispersion and spontaneous generation of anisotropic phases
Using the bosonization approach we study fermionic systems with a nonlinear
dispersion relation in dimension d>2. We explicitly show how the band curvature
gives rise to interaction terms in the bosonic version of the model. Although
these terms are perturbatively irrelevant in relation to the Landau Fermi
liquid fixed point, they become relevant perturbations when instabilities take
place. Using a coherent state path integral technique we built up the effective
action that governs the dynamics of the Fermi surface fluctuations. We consider
the combined effect of fermionic interactions and band curvature on possible
anisotropic phases triggered by negative Landau parameters. In particular we
study in some detail the phase diagram for the isotropic/nematic/hexatic
quantum phase transition.Comment: RevTeX4, 9 pages, 2 eps figures, Final version as appeared in
Phys.Rev.
Vacancy induced zero energy modes in graphene stacks: The case of ABC trilayer
The zero energy modes induced by vacancies in ABC stacked trilayer graphene
are investigated. Depending on the position of the vacancy, a new zero energy
solution is realised, different from those obtained in multilayer compounds
with Bernal stacking. The electronic modification induced in the sample by the
new vacancy states is characterised by computing the local density of states
and their localisation properties are studied by the inverse participation
ratio. We also analyse the situation in the presence of a gap in the spectrum
due to a perpendicular electric field.Comment: 6 pages, 4 figures Published in special issue: Exploring Graphene,
Recent Research Advance
The Thermodynamics of Quantum Systems and Generalizations of Zamolodchikov's C-theorem
In this paper we examine the behavior in temperature of the free energy on
quantum systems in an arbitrary number of dimensions. We define from the free
energy a function of the coupling constants and the temperature, which in
the regimes where quantum fluctuations dominate, is a monotonically increasing
function of the temperature. We show that at very low temperatures the system
is controlled by the zero-temperature infrared stable fixed point while at
intermediate temperatures the behavior is that of the unstable fixed point. The
function displays this crossover explicitly. This behavior is reminiscent
of Zamolodchikov's -theorem of field theories in 1+1 dimensions. Our results
are obtained through a thermodynamic renormalization group approach. We find
restrictions on the behavior of the entropy of the system for a
-theorem-type behavior to hold. We illustrate our ideas in the context of a
free massive scalar field theory, the one-dimensional quantum Ising Model and
the quantum Non-linear Sigma Model in two space dimensions. In regimes in which
the classical fluctuations are important the monotonic behavior is absent.Comment: 25 pages, LateX, P-92-10-12
``X-Ray Edge'' Singularities in Nanotubes and Quantum Wires with Multiple Subbands
Band theory predicts an inverse square root van Hove singularity in the
tunneling density of states at the minimum energy of an unoccupied subband in a
one-dimensional quantum wire. With interactions, an orthogonality catastrophe
analogous to the x-ray edge effect for core levels in a metal strongly reduces
this singularity by a power B of the energy above threshold, with B
approximately 0.3 for typical carbon nanotubes. Despite the anomalous tunneling
characteristic, good quasiparticles corresponding to the unoccupied subband
states do exist.Comment: 4 page
Noncritical M-Theory in 2+1 Dimensions as a Nonrelativistic Fermi Liquid
We claim that the dynamics of noncritical string theories in two dimensions
is related to an underlying noncritical version of M-theory, which we define in
terms of a double-scaled nonrelativistic Fermi liquid in 2+1 dimensions. After
reproducing Type 0A and 0B string theories as solutions, we study the natural
M-theory vacuum. The vacuum energy of this solution can be evaluated exactly,
its form suggesting a duality to the Debye model of phonons in a melting solid,
and a possible topological nature of the theory. The physical spacetime is
emergent in this theory, only for states that admit a hydrodynamic description.
Among the solutions of the hydrodynamic equations of motion for the Fermi
surface, we find families describing the decay of one two-dimensional string
theory into another via an intermediate M-theory phase.Comment: 47 pages, 1 figure; v2: typos corrected, references adde
The Fermi Liquid as a Renormalization Group Fixed Point: the Role of Interference in the Landau Channel
We apply the finite-temperature renormalization-group (RG) to a model based
on an effective action with a short-range repulsive interaction and a rotation
invariant Fermi surface. The basic quantities of Fermi liquid theory, the
Landau function and the scattering vertex, are calculated as fixed points of
the RG flow in terms of the effective action's interaction function. The
classic derivations of Fermi liquid theory, which apply the Bethe-Salpeter
equation and amount to summing direct particle-hole ladder diagrams, neglect
the zero-angle singularity in the exchange particle-hole loop. As a
consequence, the antisymmetry of the forward scattering vertex is not
guaranteed and the amplitude sum rule must be imposed by hand on the components
of the Landau function. We show that the strong interference of the direct and
exchange processes of particle-hole scattering near zero angle invalidates the
ladder approximation in this region, resulting in temperature-dependent
narrow-angle anomalies in the Landau function and scattering vertex. In this RG
approach the Pauli principle is automatically satisfied. The consequences of
the RG corrections on Fermi liquid theory are discussed. In particular, we show
that the amplitude sum rule is not valid.Comment: 25 pages, RevTeX 3.
Effect of disorder on the ground-state properties of graphene
We calculate the ground-state energy of Dirac electrons in graphene in the
presence of disorder. We take randomly distributed charged impurities at a
fixed distance from the graphene sheet and surface fluctuations (ripples) as
the main scattering mechanisms. Mode-coupling approach to scattering rate and
random-phase approximation for ground-state energy incorporating the many-body
interactions and the disorder effects yields good agreement with experimental
inverse compressibility.Comment: Extended introduction and discussion. To appear in Phys. Rev.
Electronic Properties of Two-Dimensional Carbon
We present a theoretical description of the electronic properties of graphene
in the presence of disorder, electron-electron interactions, and particle-hole
symmetry breaking. We show that while particle-hole asymmetry, long-range
Coulomb interactions, and extended defects lead to the phenomenon of
self-doping, local defects determine the transport and spectroscopic
properties. Our results explain recent experiments in graphitic devices and
predict new electronic behavior.Comment: 4 pages, 5 figures. The paper was originally submitted on May, 12th,
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