2,219 research outputs found
Exact Jastrow-Slater wave function for the one-dimensional Luttinger model
We show that it is possible to describe the ground state of the Luttinger
model in terms of a Jastrow-Slater wave function. Moreover, our findings reveal
that one-particle excitations and their corresponding dynamics can be
faithfully represented only when a Jastrow factor of a similar form is applied
to a coherent superposition of many Slater determinants. We discuss the
possible relevance of this approach for the theoretical description of
photoemission spectra in higher dimensionality, where the present wave function
can be straightforwardly generalized and can be used as a variational ansatz,
that is exact for the 1D Luttinger model.Comment: 10 pages, one figure, to appear in Phys. Rev.
Exact numerical diagonalization of one-dimensional interacting electrons nonadiabatically coupled to phonons
We study the role of non-adiabatic Holstein electron-phonon coupling on the
neutral-ionic phase transition of charge transfer crystals which can be tuned
from continuous to discontinuous, using exact numerical diagonalization. The
variation of electronic properties through the transition is smoothed by
nonadiabaticity. Lattice properties are strongly affected, and we observe both
squeezing and antisqueezing, depending on details of the adiabatic potentials,
and identify the quantum uncertainty of the phonons as the most sensitive
measure of nonadiabaticity. The adiabatic limit is regular for a continuous
transition but turns out completely inadequate near a discontinuous transition.
The relevance of coherent state approaches is assessed critically.Comment: latex manuscript (7 pages), 3 eps figures; revised version, better
discussion, one figure replaced; to be published in Europhys. Let
Does Luttinger liquid behaviour survive in an atomic wire on a surface?
We form a highly simplified model of an atomic wire on a surface by the
coupling of two one-dimensional chains, one with electron-electron interactions
to represent the wire and and one with no electron-electron interactions to
represent the surface. We use exact diagonalization techniques to calculate the
eigenstates and response functions of our model, in order to determine both the
nature of the coupling and to what extent the coupling affects the Luttinger
liquid properties we would expect in a purely one-dimensional system. We find
that while there are indeed Luttinger liquid indicators present, some residual
Fermi liquid characteristics remain.Comment: 14 pages, 7 figures. Submitted to J Phys
Conduction States with Vanishing Dimerization in Pt Nanowires on Ge(001) Observed with Scanning Tunneling Microscopy
The low-energy electronic properties of one-dimensional nanowires formed by
Pt atoms on Ge(001) are studied with scanning tunneling microscopy down to the
millivolt-regime. The chain structure exhibits various dimerized elements at
high tunneling bias, indicative of a substrate bonding origin rather than a
charge density wave. Unexpectedly, this dimerization becomes vanishingly small
when imaging energy windows close to the Fermi level with adequately low
tunneling currents. Evenly spaced nanowire atoms emerge which are found to
represent conduction states. Implications for the metallicity of the chains are
discussed.Comment: 4 pages, 4 figure
Renormalization-group study of a magnetic impurity in a Luttinger liquid
A generalized Anderson model for a magnetic impurity in an interacting
one-dimensional electron gas is studied via a mapping onto a classical Coulomb
gas. For weak potential scattering, the local-moment parameter regime expands
as repulsive bulk interactions become stronger, but the Kondo scale for the
quenching of the impurity moment varies nonmonotonically. There also exist two
regimes dominated by backward potential scattering: one in which the impurity
is nonmagnetic, and another in which an unquenched local moment survives down
to very low temperatures.Comment: REVTeX, 4 pages, 3 epsf-embedded EPS figure
IUE absorption studies of broad- and narrow-line gas in Seyfert galaxies
The interstellar medium of a galaxy containing an active nucleus may be profoundly affected by the high energy (X-ray, EUV) continuum flux emanating from the central source. The energetic source may photoionize the interstellar medium out to several kiloparsecs, thereby creating a global H II region. The International Ultraviolet Explorer (IUE) satellite has attempted to observe in several Seyfert galaxies (NGC 3516, NGC 4151, NGC 1068, 3C 120) the narrow absorption lines expected from such global H II regions. Instead, in two of the galaxies (NGC 3516, NGC 4151) broad, variable absorption lines at C IV lambda 1550, N V lambda 1240, and Si IV lambda 1400 were found, as well as weaker absorption features at O I lambda 1302 and C II lambda 1335. These features swamp any possible global H II region absorption. Such broad absorption features have previously been observed in IUE data, but their origin is still not well understood
Spin-charge separation and simultaneous spin and charge Kondo effect
We study the spin-charge separation in a Kondo-like model for an impurity
with a spin and a charge (isospin) degree of freedom coupled to a single
conduction channel (the ``spin-charge'' Kondo model). We show that the spin and
charge Kondo effects can occur simultaneously at any coupling strength. In the
continuum (wide-band or weak coupling) limit, the Kondo screening in each
sector is independent, while at finite bandwidth and strong coupling the
lattice effects lead to a renormalization of the effective Kondo exchange
constants; nevertheless, universal spin and charge Kondo effects still occur.
We find similar behavior in the two-impurity Anderson model with positive and
negative electron-electron interaction and in the two-impurity
Anderson-Holstein model with a single phonon mode. We comment on the
applicability of such models to describe the conductance of deformable
molecules with a local magnetic moment.Comment: 13 pages, 11 figure
Anomalous temperature dependence of the single-particle spectrum in the organic conductor TTF-TCNQ
The angle-resolved photoemission spectrum of the organic conductor TTF-TCNQ
exhibits an unusual transfer of spectral weight over a wide energy range for
temperatures 60K<T<260K. In order to investigate the origin of this finding,
here we report numerical results on the single-particle spectral weight
A(k,omega) for the one-dimensional (1D) Hubbard model and, in addition, for the
1D extended Hubbard and the 1D Hubbard-Holstein models. Comparisons with the
photoemission data suggest that the 1D Hubbard model is not sufficient for
explaining the unusual T dependence, and the long-range part of the Coulomb
repulsion also needs to be included.Comment: 4 pages, 4 figure
Assessment of the GW Approximation using Hubbard Chains
We investigate the performance of the GW approximation by comparison to exact results for small model systems. The role of the chemical potentials in Dyson's equation as well as the consequences of numerical resonance broadening are examined, and we show how a proper treatment can improve computational implementations of many-body perturbation theory in general. GW and exchange-only calculations are performed over a wide range of fractional band fillings and correlation strengths. We thus identify the physical situations where these schemes are applicable
Phase diagram of an asymmetric spin ladder
We investigate an asymmetric zig-zag spin ladder with different exchange
integrals on both legs using bosonization and renormalization group. When the
leg exchange integrals and frustration both are sufficiently small,
renormalization group analysis shows that the Heisenberg critical point flows
to an intermediate-coupling fixed point with gapless excitations and a
vanishing spin velocity. When they are large, a spin gap opens and a dimer
liquid is realized. Here, we find a continuous manifold of Hamiltonians with
dimer product ground states, interpolating between the Majumdar-Ghosh and
sawtooth spin-chain model.Comment: 4 pages, 2 EPS figures, to be published in PR
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