2,308 research outputs found
Determining the Electron-Phonon Coupling Strength in Correlated Electron Systems from Resonant Inelastic X-ray Scattering
We show that high resolution Resonant Inelastic X-ray Scattering (RIXS)
provides direct, element-specific and momentum-resolved information on the
electron-phonon (e-p) coupling strength. Our theoretical analysis demonstrates
that the e-p coupling can be extracted from RIXS spectra by determining the
differential phonon scattering cross section. An alternative, very direct
manner to extract the coupling is to use the one and two-phonon loss ratio,
which is governed by the e-p coupling strength and the core-hole life-time.
This allows measurement of the e-p coupling on an absolute energy scale.Comment: 4 pages, 3 figure
Non conventional screening of the Coulomb interaction in low dimensional and finite size system
We study the screening of the Coulomb interaction in non polar systems by
polarizable atoms. We show that in low dimensions and small finite size systems
this screening deviates strongly from that conventionally assumed. In fact in
one dimension the short range interaction is strongly screened and the long
range interaction is anti-screened thereby strongly reducing the gradient of
the Coulomb interaction and therefore the correlation effects. We argue that
this effect explains the success of mean field single particle theories for
large molecules.Comment: 4 pages, 5 figure
Orbital order in classical models of transition-metal compounds
We study the classical 120-degree and related orbital models. These are the
classical limits of quantum models which describe the interactions among
orbitals of transition-metal compounds. We demonstrate that at low temperatures
these models exhibit a long-range order which arises via an "order by disorder"
mechanism. This strongly indicates that there is orbital ordering in the
quantum version of these models, notwithstanding recent rigorous results on the
absence of spin order in these systems.Comment: 7 pages, 1 eps fi
Orbital excitations in LaMnO
We study the recently observed orbital excitations, orbitons, and treat
electron-electron correlations and lattice dynamics on equal footing. It is
shown that the orbiton energy and dispersion are determined by both
correlations and lattice-vibrations. The electron-phonon coupling causes
satellite structures in the orbiton spectral function and the elementary
excitations of the system are mixed modes with both orbital and phonon
character. It is proposed that the satellite structures observed in recent
Raman-scattering experiments on LaMnO are actually orbiton derived
satellites in the phonon spectral function, caused by the phonon-orbiton
interaction.Comment: 4 pages, 3 figures embedde
New light on magnetic excitations: indirect resonant inelastic X-ray scattering on magnons
Recent experiments show that indirect resonant inelastic X-ray scattering
(RIXS) is a new probe of spin dynamics. Here I derive the cross-section for
magnetic RIXS and determine the momentum dependent four-spin correlation
function that it measures. These results show that this technique offers
information on spin dynamics that is complementary to e.g. neutron scattering.
The RIXS spectrum of Heisenberg antiferromagnets is calculated. It turns out
that only scattering processes that involve at least two magnons are allowed.
Other selection rules imply that the scattering intensity vanishes for specific
transferred momenta , in particular for . The calculated
spectra agree very well with the experimental data.Comment: 4 pages, 3 figure
Reentrant metallic transition at a temperature above Tc at the breakdown of cooperative Jahn-Teller orbital order in perovskite manganites
We report an interesting reentrant metallic resistivity pattern beyond a
characteristic temperature T* which is higher than other such characteristic
transition temperatures like T(c)(Curie point), T(N) (Neel point), T(CO)
(charge order onset point) or T(OO) (orbital order onset point) in a range of
rare-erath perovskite manganites (RE(1-x)A(x)MnO(3); RE = La, Nd, Y; A = Sr,
Ca; x = 0.0-0.5). Such a behavior is normally observed in doped manganites with
doping level (x) higher than the critical doping level x(c) (= 0.17-0.22)
required for the metallic ground state to emerge and hence in a system where
cooperative Jahn-Teller orbital order has already undergone a breakdown.
However, the observation made in the La(1-x)Ca(x)MnO(3) (x = 0.0-0.5) series
turns out to be an exception to this general trend.Comment: 15 pages including 3 figures; pdf onl
Photoemission spectra of LaMnO3 controlled by orbital excitations
We investigate the spectral function of a hole moving in the orbital-ordered
ferromagnetic planes of LaMnO, and show that it depends critically on the
type of orbital ordering. While the hole does not couple to the spin
excitations, it interacts strongly with the excitations of orbitals
(orbitons), leading to new type of quasiparticles with a dispersion on the
orbiton energy scale and with strongly enhanced mass and reduced weight.
Therefore we predict a large redistribution of spectral weight with respect to
the bands found in local density approximation (LDA) or in LDA+U.Comment: 4 pages, 4 figures, 3 figures embedded, figure 3 correcte
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