1,409 research outputs found
Exact analytic results for the Gutzwiller wave function with finite magnetization
We present analytic results for ground-state properties of Hubbard-type
models in terms of the Gutzwiller variational wave function with non-zero
values of the magnetization m. In dimension D=1 approximation-free evaluations
are made possible by appropriate canonical transformations and an analysis of
Umklapp processes. We calculate the double occupation and the momentum
distribution, as well as its discontinuity at the Fermi surface, for arbitrary
values of the interaction parameter g, density n, and magnetization m. These
quantities determine the expectation value of the one-dimensional Hubbard
Hamiltonian for any symmetric, monotonically increasing dispersion epsilon_k.
In particular for nearest-neighbor hopping and densities away from half filling
the Gutzwiller wave function is found to predict ferromagnetic behavior for
sufficiently large interaction U.Comment: REVTeX 4, 32 pages, 8 figure
Quantum phase transitions and collapse of the Mott gap in the dimensional half-filled Hubbard model
We study the low-energy asymptotics of the half-filled Hubbard model with a
circular Fermi surface in continuous dimensions, based on the
one-loop renormalization-group (RG) method. Peculiarity of the
dimensions is incorporated through the mathematica structure of the elementary
particle-partcile (PP) and particle-hole (PH) loops: infrared logarithmic
singularity of the PH loop is smeared for . The RG flows indicate
that a quantum phase transition (QPT) from a metallic phase to the Mott
insulator phase occurs at a finite on-site Coulomb repulsion for
. We also discuss effects of randomness.Comment: 12 pages, 10 eps figure
Correlation and surface effects in Vanadium Oxides
Recent photoemission experiments have shown strong surface modifications in
the spectra from vanadium oxides as (V,Cr)_2O_3 or
(Sr,Ca)VO_3. The effective mass is enhanced at the surface and the coherent
part of the surface spectrum is narrowed as compared to the bulk. The
quasiparticle weight is more sensitive at the surface than in the bulk against
bandwidth variations. We investigate these effects theoretically considering
the single-band Hubbard model for a film geometry. A simplified dynamical
mean-field scheme is used to calculate the main features of the interacting
layer-dependent spectral function. It turns out that the experimentally
confirmed effects are inherent properties of a system of strongly correlated
electrons. The reduction of the weight and the variance of the coherent part of
the surface spectrum can be traced back to the reduced surface coordination
number. Surface correlation effects can be strongly amplified by changes of the
hopping integrals at the surface.Comment: to appear in PRB; 8 pages, 6 figure
Many-body position operator in lattice fermionic systems with periodic boundary conditions
A total position operator in the position representation is derived for
lattice fermionic systems with periodic boundary conditions. The operator is
shown to be Hermitian, the generator of translations in momentum space, and its
time derivative is shown to correspond to the total current operator in a
periodic system. The operator is such that its moments can be calculated up to
any order. To demonstrate its utility finite size scaling is applied to the
Brinkman-Rice transition as well as metallic and insulating Gutzwiller
wavefunctions.Comment: to appear in Journal of Physics A: Mathematical and General
(reference will be added later
Equivalence of the Falicov-Kimball and Brandt-Mielsch forms for the free energy of the infinite-dimensional Falicov-Kimball model
Falicov and Kimball proposed a real-axis form for the free energy of the
Falicov-Kimball model that was modified for the coherent potential
approximation by Plischke. Brandt and Mielsch proposed an imaginary-axis form
for the free energy of the dynamical mean field theory solution of the
Falicov-Kimball model. It has long been known that these two formulae are
numerically equal to each other; an explicit derivation showing this
equivalence is presented here.Comment: 4 pages, 1 figure, typeset with ReVTe
Hole dynamics in generalized spin backgrounds in infinite dimensions
We calculate the dynamical behaviour of a hole in various spin backgrounds in
infinite dimensions, where it can be determined exactly. We consider hypercubic
lattices with two different types of spin backgrounds. On one hand we study an
ensemble of spin configurations with an arbitrary spin probability on each
sublattice. This model corresponds to a thermal average over all spin
configurations in the presence of staggered or uniform magnetic fields. On the
other hand we consider a definite spin state characterized by the angle between
the spins on different sublattices, i.e a classical spin system in an external
magnetic field. When spin fluctuations are considered, this model describes the
physics of unpaired particles in strong coupling superconductors.Comment: Accepted in Phys. Rev. B. 18 pages of text (1 fig. included) in Latex
+ 2 figures in uuencoded form containing the 2 postscripts (mailed
separately
Efficient single-photon emission from electrically driven InP quantum dots epitaxially grown on Si(001)
The heteroepitaxy of III-V semiconductors on silicon is a promising approach
for making silicon a photonic platform for on-chip optical interconnects and
quantum optical applications. Monolithic integration of both material systems
is a long-time challenge, since different material properties lead to high
defect densities in the epitaxial layers. In recent years, nanostructures
however have shown to be suitable for successfully realising light emitters on
silicon, taking advantage of their geometry. Facet edges and sidewalls can
minimise or eliminate the formation of dislocations, and due to the reduced
contact area, nanostructures are little affected by dislocation networks. Here
we demonstrate the potential of indium phosphide quantum dots as efficient
light emitters on CMOS-compatible silicon substrates, with luminescence
characteristics comparable to mature devices realised on III-V substrates. For
the first time, electrically driven single-photon emission on silicon is
presented, meeting the wavelength range of silicon avalanche photo diodes'
highest detection efficiency
Multi-epoch Doppler tomography and polarimetry of QQ Vul
We present multi-epoch high-resolution spectroscopy and photoelectric polarimetry of the long-period polar (AM Herculis star) QQ Vul. The blue emission lines show several distinct components, the sharpest of which can unequivocally be assigned to the illuminated hemisphere of the secondary star and used to trace its orbital motion. This narrow emission line can be used in combination with Nai-absorption lines from the photosphere of the companion to build a stable long-term ephemeris for the star: inferior conjunction of the companion occurs at HJD = 244 8446.4710(5)+E×0. d 15452011(11). The polarization curves are dissimilar at different epochs, thus supporting the idea of fundamental changes of the accretion geometry, e.g. between one- and two-pole accretion modes. The linear polarization pulses display a random scatter by 0.2 phase units and are not suitable for the determination of the binary period. The polarization data suggest that the magnetic (dipolar) axis has a co-latitude of 23 ◦ , an azimuth of −50 ◦, and an orbital inclination between 50 ◦ and 70 ◦. Doppler images of blue emission and red absorption lines show a clear separatio
Electronic State and Magnetic Susceptibility in Orbitally Degenerate (J=5/2) Periodic Anderson Model
Magnetic susceptibility in a heavy fermion systemis composed of the Pauli
term (\chi_P) and the Van-Vleck term (\chi_V). The latter comes from the
interband excitation, where f-orbital degeneracy is essential. In this work, we
study \chi_P and \chi_V in the orbitally degenerate (J=5/2) periodic Anderson
model for both the metallic and insulating cases. The effect of the correlation
between f-electrons is investigated using the self-consistent second-order
perturbation theory. The main results are as follows. (i) Sixfold degenerate
model: both \chi_P and \chi_V are enhanced by a factor of 1/z (z is the
renormalization constant). (ii) Nondegenerate model: only \chi_P is enhanced by
1/z. Thus, orbital degeneracy is indispensable for enhancement of \chi_V.
Moreover, orbital degeneracy reduces the Wilson ratio and stabilizes a
nonmagnetic Fermi liquid state.Comment: 4 pages, revtex, to be published in J. Phys. Soc. Jpn. (No.8
Effective Nucleon-Nucleon Interaction and Fermi Liquid Theory
We present two novel relations between the quasiparticle interaction in
nuclear matter and the unique low momentum nucleon-nucleon interaction in
vacuum. These relations provide two independent constraints on the Fermi liquid
parameters of nuclear matter. Moreover, the new constraints define two
combinations of Fermi liquid parameters, which are invariant under the
renormalization group flow in the particle-hole channels. Using empirical
values for the spin-independent Fermi liquid parameters, we are able to compute
the major spin-dependent ones by imposing the new constraints as well as the
Pauli principle sum rules.Comment: 4 pages, 5 figures, in Proc. 11th International Conference on Recent
Progress in Many-Body Theories, Manchester, UK, July 9-13, 200
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