1,313 research outputs found
Tax Compliance and Public Goods Provision -- An Agent-based Econophysics Approach
We calculate the dynamics of tax evasion within a multi-agent econophysics
model which is adopted from the theory of magnetism and previously has been
shown to capture the main characteristics from agent-based based models which
build on the standard Allingham and Sandmo approach. In particular, we
implement a feedback of public goods provision on the decision-making of
selfish agents which aim to pursue their self interest. Our results imply that
such a feedback enhances the moral attitude of selfish agents thus reducing the
percentage of tax evasion. Two parameters govern the behavior of selfish
agents, (i) the rate of adaption to changes in public goods provision and (ii)
the threshold of perception of public goods provision. Furtheron we analyze the
tax evasion dynamics for different agent co mpositions and under the feedback
of public goods provision. We conclude that policymakers may enhance tax
compliance behavior via the threshold of perception by means of targeted public
relations.Comment: 28 pages, 3 figures, accepted for publication in the Central European
Journal of Economic Modelling and Econometric
Phase separation and long wave-length charge instabilities in spin-orbit coupled systems
We investigate a two-dimensional electron model with Rashba spin-orbit
interaction where the coupling constant depends on the electronic
density. It is shown that this dependence may drive the system unstable towards
a long-wave length charge density wave (CDW) where the associated second order
instability occurs in close vicinity to global phase separation. For very low
electron densities the CDW instability is nesting-induced and the modulation
follows the Fermi momentum . At higher density the instability criterion
becomes independent of and the system may become unstable in a broad
momentum range. Finally, upon filling the upper spin-orbit split band, finite
momentum instabilities disappear in favor of phase separation alone. We discuss
our results with regard to the inhomogeneous phases observed at the
LaAlO/SrTiO or LaTiO/SrTiO interfaces.Comment: 6 pages, 6 figure
Theory of the spin galvanic effect at oxide interfaces
The spin galvanic effect (SGE) describes the conversion of a non-equilibrium
spin polarization into a transverse charge current. Recent experiments have
demonstrated a large conversion efficiency for the two-dimensional electron gas
formed at the interface between two insulating oxides, LaAlO and SrTiO.
Here we analyze the SGE for oxide interfaces within a three-band model for the
Ti t orbitals which displays an interesting variety of effective
spin-orbit couplings in the individual bands that contribute differently to the
spin-charge conversion. Our analytical approach is supplemented by a numerical
treatment where we also investigate the influence of disorder and temperature,
which turns out to be crucial to provide an appropriate description of the
experimental data.Comment: 5 pages, 3 figure
Gutzwiller Charge Phase Diagram of Cuprates, including Electron-Phonon Coupling Effects
Besides significant electronic correlations, high-temperature superconductors
also show a strong coupling of electrons to a number of lattice modes. Combined
with the experimental detection of electronic inhomogeneities and ordering
phenomena in many high-T_c compounds, these features raise the question as to
what extent phonons are involved in the associated instabilities. Here we
address this problem based on the Hubbard model including a coupling to phonons
in order to capture several salient features of the phase diagram of hole-doped
cuprates. Charge degrees of freedom, which are suppressed by the large Hubbard
U near half-filling, are found to become active at a fairly low doping level.
We find that possible charge order is mainly driven by Fermi surface nesting,
with competition between a near-(pi,pi) order at low doping and antinodal
nesting at higher doping, very similar to the momentum structure of magnetic
fluctuations. The resulting nesting vectors are generally consistent with
photoemission and tunneling observations, evidence for charge density wave
(CDW) order in YBa_2Cu_3O_{7-delta} including Kohn anomalies, and suggestions
of competition between one- and two-q-vector nesting.Comment: This is a revised version of arXiv:1207.5715. 25 pages, 5 figures,
plus Supplement [7 pages, 7 figures], available as a pdf [click on other,
then Download Source, & extract pdf file from zip] Manuscript is under
consideration at the NJ
Dynamical charge density waves rule the phase diagram of cuprates
In the last few years charge density waves (CDWs) have been ubiquitously
observed in high-temperature superconducting cuprates and are now the most
investigated among the competing orders in the still hot debate on these
systems. A wealth of new experimental data raise several fundamental issues
that challenge the various theoretical proposals. Here, we account for the
complex experimental temperature vs. doping phase diagram and we provide a
coherent scenario explaining why different CDW onset curves are observed by
different experimental probes and seem to extrapolate at zero temperature into
seemingly different quantum critical points (QCPs) in the intermediate and
overdoped region. We also account for the pseudogap and its onset temperature
T*(p) on the basis of dynamically fluctuating CDWs. The nearly singular
anisotropic scattering mediated by these fluctuations also account for the
rapid changes of the Hall number seen in experiments and provides the first
necessary step for a possible Fermi surface reconstruction fully establishing
at lower doping. Finally we show that phase fluctuations of the CDWs, which are
enhanced in the presence of strong correlations near the Mott insulating phase,
naturally account for the disappearance of the CDWs at low doping with yet
another QCP.Comment: 13 pages, 7 figure
Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling
We propose a model for the two-dimensional electron gas formed at the
interface of oxide heterostructures that includes a Rashba spin-orbit coupling
proportional to an electric field oriented perpendicularly to the interface.
Taking into account the electron density dependence of this electric field
confining the electron gas at the interface, we report the occurrence of a
phase separation instability (signaled by a negative compressibility) for
realistic values of the spin-orbit coupling and of the electronic
band-structure parameters at zero temperature. We extend the analysis to finite
temperatures and in the presence of an in-plane magnetic field, thereby
obtaining two phase diagrams which exhibit a phase separation dome. By varying
the gating potential the phase separation dome may shrink and vanish at zero
temperature into a quantum critical point where the charge fluctuates
dynamically. Similarly the phase separation may be spoiled by a planar magnetic
field even at zero temperature leading to a line of quantum critical points.Comment: 17 pages, 17 figure
Spectroscopic evidences of quantum critical charge fluctuations in cuprates
We calculate the optical conductivity in a clean system of quasiparticles
coupled to charge-ordering collective modes. The absorption induced by these
modes may produce an anomalous frequency and temperature dependence of
low-energy optical absorption in some cuprates. However, the coupling with
lattice degrees of freedom introduces a non-universal energy scale leading to
scaling violation in low-temperature optical conductivity.Comment: Proceedings of M2S 2006. To appear in Physica
Density inhomogeneities and Rashba spin-orbit coupling interplay in oxide interfaces
There is steadily increasing evidence that the two-dimensional electron gas
(2DEG) formed at the interface of some insulating oxides like LaAlO3/SrTiO3 and
LaTiO3/SrTiO3 is strongly inhomogeneous. The inhomogeneous distribution of
electron density is accompanied by an inhomogeneous distribution of the
(self-consistent) electric field confining the electrons at the interface. In
turn this inhomogeneous transverse electric field induces an inhomogeneous
Rashba spin-orbit coupling (RSOC). After an introductory summary on two
mechanisms possibly giving rise to an electronic phase separation accounting
for the above inhomogeneity,we introduce a phenomenological model to describe
the density-dependent RSOC and its consequences. Besides being itself a
possible source of inhomogeneity or charge-density waves, the density-dependent
RSOC gives rise to interesting physical effects like the occurrence of
inhomogeneous spin-current distributions and inhomogeneous quantum-Hall states
with chiral "edge" states taking place in the bulk of the 2DEG. The
inhomogeneous RSOC can also be exploited for spintronic devices since it can be
used to produce a disorder-robust spin Hall effect.Comment: 13 pages, 15 figure
Electronic polymers and soft-matter-like broken symmetries in underdoped cuprates
Empirical evidence in heavy fermion, pnictide, and other systems suggests
that unconventional superconductivity appears associated to some form of
real-space electronic order. For the cuprates, despite several proposals, the
emergence of order in the phase diagram between the commensurate
antiferromagnetic state and the superconducting state is not well understood.
Here we show that in this regime doped holes assemble in "electronic polymers."
Within a Monte Carlo study we find, that in clean systems by lowering the
temperature the polymer melt condenses first in a smectic state and then in a
Wigner crystal both with the addition of inversion symmetry breaking. Disorder
blurs the positional order leaving a robust inversion symmetry breaking and a
nematic order, accompanied by vector chiral spin order and with the persistence
of a thermodynamic transition. Such electronic phases, whose properties are
reminiscent of soft-matter physics, produce charge and spin responses in good
accord with experiments.Comment: 10 pages, 4 figures plus supplementary informatio
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