23 research outputs found
Income tax evasion dynamics: Evidence from an agent-based econophysics model
We analyze income tax evasion dynamics in a standard model of statistical mechanics, the Ising model of ferromagnetism. However, in contrast to previous research, we use an inhomogeneous multi-dimensional Ising model where the local degrees of freedom (agents) are subject to a specific social temperature and coupled to external fields which govern their social behavior. This new modeling frame allows for analyzing large societies of four different and interacting agent types. As a second novelty, our model may reproduce results from agent-based models that incorporate standard Allingham and Sandmo tax evasion features as well as results from existing two-dimensional Ising based tax evasion models. We then use our model for analyzing income tax evasion dynamics under different enforcement scenarios and point to some policy implications. --tax evasion,tax compliance,Ising Model,econophysics,numerical simulation
Theory of charge-spin conversion at oxide interfaces: The inverse spin-galvanic effect
We evaluate the non-equilibrium spin polarization induced by an applied
electric field for a tight-binding model of electron states at oxides
interfaces in LAO/STO heterostructures. By a combination of analytic and
numerical approaches we investigate how the spin texture of the electron
eigenstates due to the interplay of spin-orbit coupling and inversion asymmetry
determines the sign of the induced spin polarization as a function of the
chemical potential or band filling, both in the absence and presence of local
disorder. With the latter, we find that the induced spin polarization evolves
from a non monotonous behavior at zero temperature to a monotonous one at
higher temperature. Our results may provide a sound framework for the
interpretation of recent experiments.Comment: Submitted to Proceedings of SPIE Nanoscience + Engineering 2018,
Spintronics XI, 23 pages, 9 figure
Intrinsic spin Hall effect in systems with striped spin-orbit coupling
The Rashba spin-orbit coupling arising from structure inversion asymmetry
couples spin and momentum degrees of freedom providing a suitable (and very
intensively investigated) environment for spintronic effects and devices. Here
we show that in the presence of strong disorder, non-homogeneity in the
spin-orbit coupling gives rise to a finite spin Hall conductivity in contrast
with the corresponding case of a homogeneous linear spin-orbit coupling. In
particular, we examine the inhomogeneity arising from a striped structure for a
two-dimensional electron gas, affecting both density and Rashba spin-orbit
coupling. We suggest that this situation can be realized at oxide interfaces
with periodic top gating.Comment: 9 pages, 8 figure
Manipulating Plasma Excitations with Terahertz Light Pulses in Superconducting Cuprates
Layered cuprates offer a preferential playground for optical non-linearity
thanks to the emergence, below Tc, of soft out-of-plane Josephson plasmons. The
hallmark of such a non-linearity is the observation of Third Harmonic
Generation, that has been theoretically understood as a sum-frequency process
involving a two-plasmon excitation. However, recent experiments in cuprates
with two planes per unit cell challenge this interpretation, due to the lack of
resonant response at the temperature where the driving frequency matches the
plasma energy scale, as observed instead in single-layer cuprates. Here we show
that such an apparent discrepancy in bilayer systems can be resolved by taking
into account the combined effect of light polarization and Josephson-coupling
anisotropy on setting the energy range where three-dimensional layered plasma
modes can be resonantly excited. Our results offer a novel perspective on the
possibility to tune on demand high-harmonic generation by artificially
designing Josephson heterostructures
Strange metal behaviour from charge density fluctuations in cuprates
Besides the mechanism responsible for high critical temperature superconductivity, the grand unresolved issue of the cuprates is the occurrence of a strange metallic state above the so-called pseudogap temperature T-*. Even though such state has been successfully described within a phenomenological scheme, the so-called Marginal Fermi-Liquid theory, a microscopic explanation is still missing. However, recent resonant X-ray scattering experiments identified a new class of charge density fluctuations characterized by low characteristic energies and short correlation lengths, which are related to the well-known charge density waves. These fluctuations are present over a wide region of the temperature-vs-doping phase diagram and extend well above T-*. Here we investigate the consequences of charge density fluctuations on the electron and transport properties and find that they can explain the strange metal phenomenology. Therefore, charge density fluctuations are likely the long-sought microscopic mechanism underlying the peculiarities of the metallic state of cuprates. The strange metallic state of cuprates occurring in a broad region of their phase diagram outside the superconducting and pseudogapped regions remains a mystery. Here the authors consider the charge density fluctuations recently discovered in resonant X-ray experiments as a possible source of scattering and show that these fluctuations can account for the strange metallic behavior
Revealing novel aspects of light-matter coupling in terahertz two-dimensional coherent spectroscopy: the case of the amplitude mode in superconductors
Recently developed terahertz (THz) two-dimensional coherent spectroscopy
(2DCS) is a powerful technique to obtain materials information in a fashion
qualitatively different from other spectroscopies. Here, we utilized THz 2DCS
to investigate the THz nonlinear response of conventional superconductor NbN.
Using broad-band THz pulses as light sources, we observed a third-order
nonlinear signal whose spectral components are peaked at twice the
superconducting gap energy . With narrow-band THz pulses, a THz
nonlinear signal was identified at the driving frequency and exhibited
a resonant enhancement at temperature when . General
theoretical considerations show that such a resonance can only arise from a
disorder-activated paramagnetic coupling between the light and the electronic
current. This proves that the nonlinear THz response can access processes
distinct from the diamagnetic Raman-like density fluctuations, which are
believed to dominate the nonlinear response at optical frequencies in metals.
Our numerical simulations reveal that even for a small amount of disorder, the
resonance is dominated by the superconducting amplitude mode
over the entire investigated disorder range. This is in contrast to other
resonances, whose amplitude-mode contribution depends on disorder. Our findings
demonstrate the unique ability of THz 2DCS to explore collective excitations
inaccessible in other spectroscopies
Characterization of animal models for primary sclerosing cholangitis (PSC)
SummaryPrimary sclerosing cholangitis (PSC) is a chronic cholangiopathy characterized by biliary fibrosis, development of cholestasis and end stage liver disease, high risk of malignancy, and frequent need for liver transplantation. The poor understanding of its pathogenesis is also reflected in the lack of effective medical treatment. Well-characterized animal models are utterly needed to develop novel pathogenetic concepts and study new treatment strategies. Currently there is no consensus on how to evaluate and characterize potential PSC models, which makes direct comparison of experimental results and effective exchange of study material between research groups difficult. The International Primary Sclerosing Cholangitis Study Group (IPSCSG) has therefore summarized these key issues in a position paper proposing standard requirements for the study of animal models of PSC
Income Tax Evasion Dynamics: Evidence from an Agent-based Econophysics Model
We analyze income tax evasion dynamics in a standard model of statistical mechanics, the Ising model of ferromagnetism. However, in contrast to previous research, we use an inhomogeneous multi-dimensional Ising model where the local degrees of freedom (agents) are subject to a specific social temperature and coupled to external fields which govern their social behavior. This new modeling frame allows for analyzing large societies of four different and interacting agent types. As a second novelty, our model may reproduce results from agent-based models that incorporate standard Allingham and Sandmo tax evasion features as well as results from existing two-dimensional Ising based tax evasion models. We then use our model for analyzing income tax evasion dynamics under different enforcement scenarios and point to some policy implications.