62 research outputs found
Dual-Path Mechanism for Catalytic Oxidation of Hydrogen on Platinum Surfaces
The catalytic formation of water from adsorbed hydrogen and oxygen atoms on Pt(111) was studied with scanning tunneling microscopy and high resolution electron energy loss spectroscopy. The known complexity of this reaction is explained by the strongly temperature dependent lifetime of the product H2O molecules on the surface. Below the desorption temperature water reacts with unreacted O adatoms to OHad, leading to an autocatalytic process; at higher temperatures sequential addition of H adatoms to Oad with normal kinetics takes place
Open t-J chain with boundary impurities
We study integrable boundary conditions for the supersymmetric t-J model of
correlated electrons which arise when combining static scattering potentials
with dynamical impurities carrying an internal degree of freedom. The latter
differ from the bulk sites by allowing for double occupation of the local
orbitals. The spectrum of the resulting Hamiltonians is obtained by means of
the algebraic Bethe Ansatz.Comment: LaTeX2e, 9p
Friedel oscillations in one-dimensional metals: from Luttinger's theorem to the Luttinger liquid
Charge density and magnetization density profiles of one-dimensional metals
are investigated by two complementary many-body methods: numerically exact
(Lanczos) diagonalization, and the Bethe-Ansatz local-density approximation
with and without a simple self-interaction correction. Depending on the
magnetization of the system, local approximations reproduce different Fourier
components of the exact Friedel oscillations.Comment: 3 pages, 3 figures, Manuscript accepted by Journal of Magnetism and
Magnetic Materials, special issue for LAWMMM 2007 conferenc
Vibrational and structural properties of OH adsorbed on Pt(111)
OH species adsorbed on Pt(111) were studied in a combined investigation using scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS). OH was formed by two different reactions, by reaction of H2O with O, and as an intermediate in the reaction of O with hydrogen to H2O. In both cases, two ordered OH phases were observed, a (√3×√3)R30° and a (3×3) structure, for which models are proposed. Both structures have OH coverages of 2/3, and their formation is driven by hydrogen bond formation between the adparticles; the OH adsorption site is most likely on top. OH molecules at defects in the adlayer, in particular at island edges, are spectroscopically distinguishable and contribute significantly to the vibrational spectra in disordered OH layers. This is important for the water formation reaction, where the OH islands are small. The discrepancies between previous HREELS studies on OH can be explained by the different degree of order under the various formation conditions
New solutions to the Reflection Equation and the projecting method
New integrable boundary conditions for integrable quantum systems can be
constructed by tuning of scattering phases due to reflection at a boundary and
an adjacent impurity and subsequent projection onto sub-spaces. We illustrate
this mechanism by considering a gl(m<n)-impurity attached to an open
gl(n)-invariant quantum chain and a Kondo spin S coupled to the supersymmetric
t-J model.Comment: Latex2e, no figure
Quantum integrability and exact solution of the supersymmetric U model with boundary terms
The quantum integrability is established for the one-dimensional
supersymmetric model with boundary terms by means of the quantum inverse
scattering method. The boundary supersymmetric chain is solved by using the
coordinate space Bethe ansatz technique and Bethe ansatz equations are derived.
This provides us with a basis for computing the finite size corrections to the
low lying energies in the system.Comment: 4 pages, RevTex. Some cosmetic changes. The version to appear in
Phys. Rev.
Integrability of the Heisenberg Chains with Boundary Impurities and Their Bethe Ansatz
In this paper, we show the integrability of spin-1/2 XXZ Heisenberg chain
with two arbitrary spin boundary Impurities. By using the fusion method, we
generalize it to the spin-1 XXZ chain. Then the eigenvalues of Hamiltonians of
these models are obtained by the means of Bethe ansatz method.Comment: 13 pages, latex, no figures, to be appeared in J.Phys.
Friedel Oscillations in the Open Hubbard Chain
Using the Density Matrix Renormalization Group (DMRG), we calculate critical
exponents for the one-dimensional Hubbard model with open boundary conditions
with and without additional boundary potentials at both ends. A direct
comparison with open boundary condition Bethe Ansatz calculations provides a
good check for the DMRG calculations on large system sizes. On the other hand,
the DMRG calculations provide an independent check of the predictions of
Conformal Field Theory, which are needed to obtain the critical exponents from
the Bethe Ansatz. From Bethe Ansatz we predict the behaviour of the
1/L-corrected mean value of the Friedel oscillations (for the density and the
magnetization) and the characteristic wave vectors, and show numerically that
these conjectures are fulfilled with and without boundary potentials. The
quality of the numerical results allows us to determine, for the first time,
the behaviour of the coefficients of the Friedel oscillations as a function of
the the Hubbard interaction.Comment: 12 pages, 16 figures; submitted to Phys. Rev.
Energetics and Vibrational States for Hydrogen on Pt(111)
We present a combination of theoretical calculations and experiments for the
low-lying vibrational excitations of H and D atoms adsorbed on the Pt(111)
surface. The vibrational band states are calculated based on the full
three-dimensional adiabatic potential energy surface obtained from first
principles calculations. For coverages less than three quarters of a monolayer,
the observed experimental high-resolution electron peaks at 31 and 68meV are in
excellent agreement with the theoretical transitions between selected bands.
Our results convincingly demonstrate the need to go beyond the local harmonic
oscillator picture to understand the dynamics of this system.Comment: In press at Phys. Rev. Lett - to appear in April 200
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