2,481 research outputs found
Exact Spectral Functions of a Non Fermi Liquid in 1 Dimension
We study the exact one electron propagator and spectral function of a
solvable model of interacting electrons due to Schulz and Shastry. The solution
previously found for the energies and wave functions is extended to give the
spectral functions, which turn out to be computable, interesting and non
trivial. They provide one of the few examples of cases where the spectral
functions are known asymptotically as well as exactly.Comment: 14 pages, 5 figures, revte
Spectral microscopic mechanisms and quantum phase transitions in a 1D correlated problem
In this paper we study the dominant microscopic processes that generate
nearly the whole one-electron removal and addition spectral weight of the
one-dimensional Hubbard model for all values of the on-site repulsion . We
find that for the doped Mott-Hubbard insulator there is a competition between
the microscopic processes that generate the one-electron upper-Hubbard band
spectral-weight distributions of the Mott-Hubbard insulating phase and
finite-doping-concentration metallic phase, respectively. The spectral-weight
distributions generated by the non-perturbative processes studied here are
shown elsewhere to agree quantitatively for the whole momentum and energy
bandwidth with the peak dispersions observed by angle-resolved photoelectron
spectroscopy in quasi-one-dimensional compounds.Comment: 18 pages, 2 figure
Negative thermal expansion in the plateau state of a magnetically-frustrated spinel
We report on negative thermal expansion (NTE) in the high-field,
half-magnetization plateau phase of the frustrated magnetic insulator CdCr2O4.
Using dilatometry, we precisely map the phase diagram at fields of up to 30T,
and identify a strong NTE associated with the collinear half-magnetization
plateau for B > 27T. The resulting phase diagram is compared with a microscopic
theory for spin-lattice coupling, and the origin of the NTE is identified as a
large negative change in magnetization with temperature, coming from a
nearly-localised band of spin excitations in the plateau phase. These results
provide useful guidelines for the discovery of new NTE materials.Comment: 6 pages, 2 figure
Mixed-valence state in Yb2CuGe6
We present here temperature dependent X-ray photoemission measurements on polycrystalline Yb2CuGe6. The analysis of these data shows the change in the effective valence, determined directly from the 4f intensity
ratio, as a function of temperature
Superconductivity Driven by Chain Coupling and Electronic Correlations
We present an analysis of a system of weakly coupled Hubbard chains based on
combining an exact study of spectral functions of the uncoupled chain system
with a renormalization group method for the coupled chains. For low values of
the onsite repulsion and of the doping , the leading instability is
towards a superconducting state. The process includes excited states above a
small correlation pseudogap. Similar features appear in extended Hubbard models
in the vicinity of commensurate fillings. Our theoretical predictions are
consistent with the phase diagram observed in the (TMTTF)X and (TMTSF)X
series of organic compounds.Comment: 7 pages, 2 figure
Electronic structure of CePtIn and LaPtIn compounds
The electronic structure of the ternary RPtIn (R = La, Ce) compounds, which crystallize in the hexagonal
ZrNiAl-type structure, was studied by X-ray photoelectron spectroscopy measurements and calculation using the
ab initio methods (linear mu n-tin orbital in the atomic sphere approximation, full potential linear mu n-tin
orbital, full potential linear orbital). The results showed that the valence band in these compounds is formed by
the Pt 5d and In 5s and 5p states. The band calculations with spin orbit coupling have shown that the Ce 4f
peaks consist of two peaks above the Fermi level that correspond to the Ce 4f7=2 and 4f5=2 doublet and wide peaks corresponding to the La 4f states. The analysis of Ce 3d spectra on the basis of the Gunnarsson Schönhammer model gives hybridization of 4f orbitals with the conduction electron band equal to 170 meV
Electronic structure of CePtIn and LaPtIn compounds
The electronic structure of the ternary RPtIn (R = La, Ce) compounds, which crystallize in the hexagonal
ZrNiAl-type structure, was studied by X-ray photoelectron spectroscopy measurements and calculation using the
ab initio methods (linear mu n-tin orbital in the atomic sphere approximation, full potential linear mu n-tin
orbital, full potential linear orbital). The results showed that the valence band in these compounds is formed by
the Pt 5d and In 5s and 5p states. The band calculations with spin orbit coupling have shown that the Ce 4f
peaks consist of two peaks above the Fermi level that correspond to the Ce 4f7=2 and 4f5=2 doublet and wide peaks corresponding to the La 4f states. The analysis of Ce 3d spectra on the basis of the Gunnarsson Schönhammer model gives hybridization of 4f orbitals with the conduction electron band equal to 170 meV
spl(2,1) dynamical supersymmetry and suppression of ferromagnetism in flat band double-exchange models
The low energy spectrum of the ferromagnetic Kondo lattice model on a N-site
complete graph extended with on-site repulsion is obtained from the underlying
spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic
ground state is realized for 1 and N+1 electrons only. We identify the large
density of states to be responsible for the suppression of the ferromagnetic
state and argue that a similar situation is encountered in the Kagome,
pyrochlore, and other lattices with flat bands in their one-particle density of
states.Comment: 7 pages, 1 figur
Susceptibility of the one-dimensional, dimerized Hubbard model
We show that the zero temperature susceptibility of the one-dimensional,
dimerized Hubbard model at quarter-filling can be accurately determined on the
basis of exact diagonalization of small clusters. The best procedure is to
perform a finite-size scaling of the spin velocity , and to calculate
the susceptibility from the Luttinger liquid relation . We
show that these results are reliable by comparing them with the analytical
results that can be obtained in the weak and strong coupling limits. We have
also used quantum Monte Carlo simulations to calculate the temperature
dependence of the susceptibility for parameters that should be relevant to the
Bechgaard salts. This shows that, used together, these numerical techniques are
able to give precise estimates of the low temperature susceptibility of
realistic one-dimensional models of correlated electrons.Comment: 10 pages, latex, figures available from the authors. To appear in
Phys. Rev. B, Rapid Comm
Electronic structure of TmPdIn
Electronic structure of a ternary TmPdIn compound, which crystallizes in the hexagonal ZrNiAl-type structure,
was studied by X-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. Density of states
in the valence band was calculated by means of the augmented plane wave/local orbital method based on density
functional theory. The results showed that the valence band is formed mainly of Tm 4f and Pd 4d states. In the
ultraviolet photoemission spectra one can distinguish Pd 4d maximum and Tm 4f multiplet peaks, which are
displaced with respect to those of pure Tm
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