5,511 research outputs found
Consumption and Cash-Flow Taxes in an International Setting
We model the effects of consumption-type taxes which differ according to the base and location of the tax. Our model incorporates a monopolist producing and selling in two countries with three sources of rent, each in a different location: a fixed factor (located with production), mobile managerial skill, and a monopoly mark-up (located with consumption). In the general case, we show that for national governments, there are tradeoffs in choosing between alternative taxes. In particular, a cash-flow tax on a source basis creates welfare-impairing distortions to production and consumption, but is incident on the owners of domestic production who may be non-resident. By contrast, a destination-based cash-flow tax does not distort behavior, but is incident only on domestic residents. In the alternative case of perfect competition, with the returns to the fixed factor accruing to domestic residents, the only distortion from the source-based tax is through the allocation of the mobile managerial skill. In this case, the sourcebased tax is also incident only on domestic residents, and is dominated by an equivalent tax on a destination basis, or by a sales tax.
Domain Patterns in the Microwave-Induced Zero-Resistance State
It has been proposed that the microwave-induced ``zero-resistance''
phenomenon, observed in a GaAs two-dimensional electron system at low
temperatures in moderate magnetic fields, results from a state with multiple
domains, in which a large local electric field \bE(\br) is oriented in
different directions. We explore here the questions of what may determine the
domain arrangement in a given sample, what do the domains look like in
representative cases, and what may be the consequences of domain-wall
localization on the macroscopic dc conductance. We consider both effects of
sample boundaries and effects of disorder, in a simple model, which has a
constant Hall conductivity, and is characterized by a Lyapunov functional.Comment: 19 pages, 5 figures; submitted to a special issue of Journal of
Statistical Physics, in honor of P. C. Hohenberg and J. S. Lange
Effective single-band models for strongly interacting fermions in an optical lattice
To test effective Hamiltonians for strongly interacting fermions in an
optical lattice, we numerically find the energy spectrum for two fermions
interacting across a Feshbach resonance in a double well potential. From the
spectrum, we determine the range of detunings for which the system can be
described by an effective lattice model, and how the model parameters are
related to the experimental parameters. We find that for a range of strong
interactions the system is well described by an effective model, and the
effective superexchange term, , can be smoothly tuned through zero on either
side of unitarity. Right at and around unitarity, an effective one-band general
Hubbard model is appropriate, with a finite and small on-site energy, due to a
lattice-induced anharmonic coupling between atoms at the scattering threshold
and a weakly bound Feshbach molecule in an excited center of mass state.Comment: 7 pages, 7 figures; minor typos correcte
Mid-IR continuous-wave fiber-laser-pumped optical parametric oscillators
We review recent developments in continuous-wave mid-infrared optical parametric oscillators pumped by fiber lasers. Such devices are potentially valuable spectroscopic sources providing high output powers and rapid, wide-range tuning in the mid-infrared molecular fingerprint region
Observability of Quantum Criticality and a Continuous Supersolid in Atomic Gases
We analyze the Bose-Hubbard model with a three-body hardcore constraint by
mapping the system to a theory of two coupled bosonic degrees of freedom. We
find striking features that could be observable in experiments, including a
quantum Ising critical point on the transition from atomic to dimer
superfluidity at unit filling, and a continuous supersolid phase for strongly
bound dimers.Comment: 4 pages, 2 figures, published version (Editor's suggestion
Dissipation-induced d-Wave Pairing of Fermionic Atoms in an Optical Lattice
We show how dissipative dynamics can give rise to pairing for two-component
fermions on a lattice. In particular, we construct a "parent" Liouvillian
operator so that a BCS-type state of a given symmetry, e.g. a d-wave state, is
reached for arbitrary initial states in the absence of conservative forces. The
system-bath couplings describe single-particle, number conserving and
quasi-local processes. The pairing mechanism crucially relies on Fermi
statistics. We show how such Liouvillians can be realized via reservoir
engineering with cold atoms representing a driven dissipative dynamics.Comment: 5 pages, 3 figures. Replaced with the published versio
Spin 3/2 dimer model
We present a parent Hamiltonian for weakly dimerized valence bond solid
states for arbitrary half-integral S. While the model reduces for S=1/2 to the
Majumdar-Ghosh Hamiltonian we discuss this model and its properties for S=3/2.
Its degenerate ground state is the most popular toy model state for discussing
dimerization in spin 3/2 chains. In particular, it describes the impurity
induced dimer phase in Cr8Ni as proposed recently. We point out that the
explicit construction of the Hamiltonian and its main features apply to
arbitrary half-integral spin S.Comment: 5+ pages, 6 figures; to appear in Europhysics Letter
Ferromagnetically coupled dimers on the distorted Shastry-Sutherland lattice: Application to (CuCl)LaNb2O7
A recent study [Tassel {\it et al.}, Phys. Rev. Lett. {\bf 105}, 167205
(2010)] has proposed a remarkable spin model for (CuCl)LaNb2O7, in which dimers
are ferromagnetically coupled to each other on the distorted Shastry-Sutherland
lattice. In this model, the intra-dimer exchange coupling J>0 is
antiferromagnetic, while the inter-dimer exchange couplings are ferromagnetic
and take different values, J_x,J_y<0, in the two bond directions. Anticipating
that the highly frustrated character of this model may lead to a wide range of
behaviors in (CuCl)LaNb2O7 and related compounds, we theoretically investigate
the ground state phase diagram of this model in detail using the following
three approaches: a strong-coupling expansion for small J_x and J_y, exact
diagonalization for finite clusters, and a Schwinger boson mean field theory.
When |J_x|, |J_y| <~ J, the system stays in a dimer singlet phase with a finite
spin gap. This state is adiabatically connected to the decoupled-dimer limit
J_x=J_y=0. We show that the magnetization process of this phase depends
crucially on the spatial anisotropy of the inter-dimer couplings. The
magnetization shows a jump or a smooth increase for weak and strong anisotropy,
respectively, after the spin gap closes at a certain magnetic field. When |J_x|
or |J_y| >~ J, quantum phase transitions to various magnetically ordered phases
(ferromagnetic, collinear stripe, and spiral) occur. The Schwinger boson
analysis demonstrates that quantum fluctuations split the classical degeneracy
of different spiral ground states. Implications for (CuCl)LaNb2O7 and related
compounds are discussed in light of our theoretical results and existing
experimental data.Comment: 21 pages, 20 figure
Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part I: Formal Developments
We develop a quantum field theoretical framework to analytically study the
three-body constrained Bose-Hubbard model beyond mean field and non-interacting
spin wave approximations. It is based on an exact mapping of the constrained
model to a theory with two coupled bosonic degrees of freedom with polynomial
interactions, which have a natural interpretation as single particles and
two-particle states. The procedure can be seen as a proper quantization of the
Gutzwiller mean field theory. The theory is conveniently evaluated in the
framework of the quantum effective action, for which the usual symmetry
principles are now supplemented with a ``constraint principle'' operative on
short distances. We test the theory via investigation of scattering properties
of few particles in the limit of vanishing density, and we address the
complementary problem in the limit of maximum filling, where the low lying
excitations are holes and di-holes on top of the constraint induced insulator.
This is the first of a sequence of two papers. The application of the formalism
to the many-body problem, which can be realized with atoms in optical lattices
with strong three-body loss, is performed in a related work [14].Comment: 21 pages, 5 figure
Effect of spatial inhomogeneity on the mapping between strongly interacting fermions and weakly interacting spins
A combined analytical and numerical study is performed of the mapping between
strongly interacting fermions and weakly interacting spins, in the framework of
the Hubbard, t-J and Heisenberg models. While for spatially homogeneous models
in the thermodynamic limit the mapping is thoroughly understood, we here focus
on aspects that become relevant in spatially inhomogeneous situations, such as
the effect of boundaries, impurities, superlattices and interfaces. We consider
parameter regimes that are relevant for traditional applications of these
models, such as electrons in cuprates and manganites, and for more recent
applications to atoms in optical lattices. The rate of the mapping as a
function of the interaction strength is determined from the Bethe-Ansatz for
infinite systems and from numerical diagonalization for finite systems. We show
analytically that if translational symmetry is broken through the presence of
impurities, the mapping persists and is, in a certain sense, as local as
possible, provided the spin-spin interaction between two sites of the
Heisenberg model is calculated from the harmonic mean of the onsite Coulomb
interaction on adjacent sites of the Hubbard model. Numerical calculations
corroborate these findings also in interfaces and superlattices, where
analytical calculations are more complicated.Comment: 7 pages, 6 figure
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