2,133 research outputs found
Efficiency = Equity and Other Musings on Economics and Sustainable Development
Conventional wisdom says that equity concerns are beyond the scope of economic analysis and that achieving equity objectives will often come at a cost in terms of efficiency. Examination of the underlying meaning of efficiency and how it is defined, however, reveals that this tension between efficiency and equity is more apparent than real. The paper also explores the application of other economic concepts to the field of sustainable development, including the use of discounting for present value, Gross Domestic Product as a measure of well-being, and rational utility maximisation vs. bounded rationality as models of human behaviour.Agricultural and Food Policy, Community/Rural/Urban Development, Environmental Economics and Policy, Land Economics/Use, Research Methods/ Statistical Methods,
Emergent Chern-Simons excitations due to electron--phonon interaction
We address the problem of Dirac fermions interacting with longitudinal
phonons. A gap in the spectrum of fermions leads to the emergence of the
Chern--Simons excitations in the spectrum of phonons. We study the effect of
those excitations on observable quantities: the phonon dispersion, the phonon
spectral density, and the Hall conductivity.Comment: 9 pages, 4 figure
Short note on the density of states in 3D Weyl semimetals
The average density of states in a disordered three-dimensional Weyl system
is discussed in the case of a continuous distribution of random scattering. Our
result clearly indicate that the average density of states does not vanish,
reflecting the absence of a critical point for a metal-insulator transition.
This calculation supports recent suggestions of an avoided quantum critical
point in the disordered three-dimensional Weyl semimetal. However, the
effective density of states can be very small such that the
saddle-approximation with a vanishing density of states might be valid for
practical cases.Comment: 5 pages, 2 figures, minor changes, additional supplemen
Perturbative analysis of the conductivity in disordered monolayer and bilayer graphene
The DC conductivity of monolayer and bilayer graphene is studied
perturbatively for different types of disorder. In the case of monolayer, an
exact cancellation of logarithmic divergences occurs for all disorder types.
The total conductivity correction for a random vector potential is zero, while
for a random scalar potential and a random gap it acquires finite corrections.
We identify the diagrams which are responsible for these corrections and
extrapolate the finite contributions to higher orders which gives us general
expressions for the conductivity of weakly disordered monolayer graphene. In
the case of bilayer graphene, a cancellation of all contributions for all types
of disorder takes place. Thus, the minimal conductivity of bilayer graphene
turns out to be very robust against disorder.Comment: 4 pages, 2 figures + supplementary material. Final version as
published with PR
Renormalized transport properties of randomly gapped 2D Dirac fermions
We investigate the scaling properties of the recently acquired fermionic
non--linear --model which controls gapless diffusive modes in a
two--dimensional disordered system of Dirac electrons beyond charge neutrality.
The transport on large scales is governed by a novel renormalizable nonlocal
field theory. For zero mean random gap, it is characterized by the absence of a
dynamic gap generation and a scale invariant diffusion coefficient. The
function of the DC conductivity, computed for this model, is in perfect
agreement with numerical results obtained previously.Comment: Version published with minor change
Conductivity of disordered 2d binodal Dirac electron gas: Effect of the internode scattering
We study the dc conductivity of a weakly disordered 2d Dirac electron gas
with two bands and two spectral nodes, employing a field theoretical version of
the Kubo--Greenwood conductivity formula. In this paper we are concerned with
the question how the internode scattering affects the conductivity. We use and
compare two established techniques for treating the disorder scattering: The
perturbation theory, there ladder and maximally crossed diagrams are summed up,
and the functional integral approach. Both turn out to be entirely equivalent.
For a large number of random potential configurations we have found only two
different conductivity scenarios. Both scenarios appear independently of
whether the disorder does or does not create the internode scattering. In
particular we do not confirm the conjecture that the internode scattering tends
to Anderson localization
Effect of Coulomb interaction on the gap in monolayer and bilayer graphene
We study effects of a repulsive Coulomb interaction on the spectral gap in
monolayer and bilayer graphene in the vicinity of the charge neutrality point
by employing the functional renormalization-group technique. In both cases
Coulomb interaction supports the gap once it is open. For monolayer graphene we
correctly reproduce results obtained previously by several authors, e.g., an
apparent logarithmic divergence of the Fermi velocity and the gap as well as a
fixed point corresponding to a quantum phase transition at infinitely large
Coulomb interaction. On the other hand, we show that the gap introduces an
additional length scale at which renormalization flow of diverging quantities
saturates. An analogous analysis is also performed for bilayer graphene with
similar results. We find an additional fixed point in the gapless regime with
linear spectrum corresponding to the vanishing electronic band mass. This fixed
point is unstable with respect to gap fluctuations and can not be reached as
soon as the gap is opened. This preserves the quadratic scaling of the spectrum
and finite electronic band mass.Comment: 6 pages, 5 figures, final version to appear at PR
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