617 research outputs found
Charged excitons in doped extended Hubbard model systems
We show that the charge transfer excitons in a Hubbard model system including
nearest neighbor Coulomb interactions effectively attain some charge in doped
systems and become visible in photoelectron and inverse photoelectron
spectroscopies. This shows that the description of a doped system by an
extended Hubbard model differs substantially from that of a simple Hubbard
model. Longer range Coulomb interactions cause satellites in the one electron
removal and addition spectra and the appearance of spectral weight if the gap
of doped systems at energies corresponding to the excitons of the undoped
systems. The spectral weight of the satellites is proportional to the doping
times the coordination number and therefore is strongly dependent on the
dimension.Comment: 10 pages revtex, 5 figures ps figures adde
t-J model of coupled CuO ladders in SrCaCuO
Starting from the proper charge transfer model for CuO coupled
ladders in SrCaCuO we derive the low energy
Hamiltonian for this system. It occurs that the widely used ladder t-J model is
not sufficient and has to be supplemented by the Coulomb repulsion term between
holes in the neighboring ladders. Furthermore, we show how a simple mean-field
solution of the derived t-J model may explain the onset of the charge density
wave with the odd period in SrCaCuO.Comment: 8 pages, 4 figures, 2 table
Single polaron properties of the breathing-mode Hamiltonian
We investigate numerically various properties of the one-dimensional (1D)
breathing-mode polaron. We use an extension of a variational scheme to compute
the energies and wave-functions of the two lowest-energy eigenstates for any
momentum, as well as a scheme to compute directly the polaron Greens function.
We contrast these results with results for the 1D Holstein polaron. In
particular, we find that the crossover from a large to a small polaron is
significantly sharper. Unlike for the Holstein model, at moderate and large
couplings the breathing-mode polaron dispersion has non-monotonic dependence on
the polaron momentum k. Neither of these aspects is revealed by a previous
study based on the self-consistent Born approximation
Drude weight and total optical weight in a t-t'-J model
We study the Drude weight D and the total optical weight K for a t-t'-J model
on a square lattice that exhibits a metallic phase-modulated antiferromagnetic
ground state close to half-filling. Within a suitable 1/N expansion that
includes leading quantum-fluctuation effects, D and K are found to increase
linearly with small hole doping away from the Mott metal-insulator transition
point at half-filling. The slow zero-sound velocity near the latter transition
identifies with the velocity of the lower-energy branch of the twofold
excitation spectrum. At higher doping values, D and K eventually saturate and
then start to decrease. These features are in qualitative agreement with
optical conductivity measurements in doped antiferromagnets.Comment: 7 pages, REVTEX file (3 Postscript figures). To appear in J. Phys.:
Condens. Mattte
Exchange Splitting and Charge Carrier Spin Polarization in EuO
High quality thin films of the ferromagnetic semiconductor EuO have been
prepared and were studied using a new form of spin-resolved spectroscopy. We
observed large changes in the electronic structure across the Curie and
metal-insulator transition temperature. We found that these are caused by the
exchange splitting of the conduction band in the ferromagnetic state, which is
as large as 0.6 eV. We also present strong evidence that the bottom of the
conduction band consists mainly of majority spins. This implies that doped
charge carriers in EuO are practically fully spin polarized.Comment: 4 pages, 5 figure
Cu -edge Resonant Inelastic X-Ray Scattering in Edge-Sharing Cuprates
We present calculations for resonant inelastic x-ray scattering (RIXS) in
edge-shared copper oxide systems, such as CuGeO and LiCuO,
appropriate for hard x-ray scattering where the photoexcited electron lies
above oxygen 2p and copper 3d orbital energies. We perform exact
diagonalizations of the multi-band Hubbard and determine the energies, orbital
character and resonance profiles of excitations which can be probed via RIXS.
We find excellent agreement with recent results on LiCuO and
CuGeO in the 2-7 eV photon energy loss range.Comment: Updated with new data, expanded 9 pages, 9 figure
Electronic depth profiles with atomic layer resolution from resonant soft x-ray reflectivity
The analysis of x-ray reflectivity data from artificial heterostructures
usually relies on the homogeneity of optical properties of the constituent
materials. However, when the x-ray energy is tuned to an absorption edge, this
homogeneity no longer exists. Within the same material, spatial regions
containing elements at resonance will have optical properties very different
from regions without resonating sites. In this situation, models assuming
homogeneous optical properties throughout the material can fail to describe the
reflectivity adequately. As we show here, resonant soft x-ray reflectivity is
sensitive to these variations, even though the wavelength is typically large as
compared to the atomic distances over which the optical properties vary. We
have therefore developed a scheme for analyzing resonant soft x-ray
reflectivity data, which takes the atomic structure of a material into account
by "slicing" it into atomic planes with characteristic optical properties.
Using LaSrMnO4 as an example, we discuss both the theoretical and experimental
implications of this approach. Our analysis not only allows to determine
important structural information such as interface terminations and stacking of
atomic layers, but also enables to extract depth-resolved spectroscopic
information with atomic resolution, thus enhancing the capability of the
technique to study emergent phenomena at surfaces and interfaces.Comment: Completely overhauled with respect to the previous version due to
peer revie
Farm-Based Programming for College Students Experiencing Food Insecurity
Student food insecurity is a concern at colleges and universities across the country, and Extension professionals can bring unique solutions to this growing problem. At Rutgers–New Brunswick, visitors to the Student Food Pantry receive vouchers for fresh produce to be redeemed at the New Brunswick Community Farmers Market. The Rutgers Gardens Student Farm makes weekly deliveries of fresh produce to the pantry, which is available at no cost to students. With creativity, Extension efforts such as master gardener programs, Supplemental Nutrition Assistance Program Education, and family and community health sciences programs can play an important role in alleviating college student food insecurity
Unraveling the Nature of Charge Excitations in LaCuO with Momentum-Resolved Cu -edge Resonant Inelastic X-ray Scattering
Results of model calculations using exact diagonalization reveal the orbital
character of states associated with different Raman loss peaks in Cu -edge
resonant inelastic X-ray scattering (RIXS) from LaCuO. The model
includes electronic orbitals necessary to highlight non-local Zhang-Rice
singlet, charge transfer and - excitations, as well as states with apical
oxygen 2 character. The dispersion of these excitations is discussed with
prospects for resonant final state wave-function mapping. A good agreement with
experiments emphasizes the substantial multi-orbital character of RIXS profiles
in the energy transfer range 1-6 eV.Comment: Original: 4.5 pages. Replaced: 4 pages and 4 figures with updated
content and reference
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