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1.
Interplay of charge, spin, orbital and lattice correlations in colossal magnetoresistance manganites
A. Weiße H. Fehske 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):487-494
We derive a realistic microscopic model for doped colossal magnetoresistance manganites, which includes the dynamics of charge,
spin, orbital and lattice degrees of freedom on a quantum mechanical level. The model respects the SU(2) spin symmetry and the full multiplet structure of the manganese ions within the cubic lattice. Concentrating on the hole
doped domain ( 0≤x≤0.5) we study the influence of the electron-lattice interaction on spin and orbital correlations by means of exact diagonalisation
techniques. We find that the lattice can cause a considerable suppression of the coupling between spin and orbital degrees
of freedom and show how changes in the magnetic correlations are reflected in dynamic phonon correlations. In addition, our
calculation gives detailed insights into orbital correlations and demonstrates the possibility of complex orbital states.
Received 4 September 2002 / Received in final form 8 November 2002 Published online 31 December 2002 相似文献
2.
Summary The screening effects of the formation of large bipolarons have been studied. It is shown that the dependence of the bipolaron
binding energy on the electron density does not change qualitatively by using different dielectric functions for describing
electron screening. The same result is found if the electron system is described as a bipolaron gas (charged bosons). 相似文献
3.
A. M. Dikandé 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):397-402
Excitations of the polaron types are investigated in the spin-1/2 quantum chain with XY exchange and Dzyaloshinsky-Moriya
interaction, both coupled to acoustic vibrations of the substrate lattice. The study is carried out via Jordan-Wigner transformation
with the help of which the spin chain is mapped onto a chain of spinless fermions. From the resulting effective fermion-lattice
Hamiltonian, the discrete equations of motion are derived. These equations are solved in the continuum limit for self-trapped
states near the bottom of the fermion spectrum interacting with long-wavelength acoustic lattice modes. The associate polaron
solution, which has a pulse shape, is shown to propagate bound to the induced lattice kink distortion by translation along
the chain at a constant velocity v. The pair can also experience an additional acceleration ϑ0 when the free fermion charge is excited above its groundstate. The polaron binding energy is strongly reduced, depending
quadratically on the ratio D/J of the Dzyaloshinsky-Moriya interaction strength D to the isotropic XY exchange interaction
J. It is also found that polaron parameters depend only on the XY spin-lattice coupling but not on the Dzyaloshinsky-Moriya
contribution. 相似文献
4.
J. Laverdière S. Jandl A. A. Mukhin V. Yu. Ivanov 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):67-72
We have studied RMnO3 manganites (R = Pr, Sm, Eu, Tb, Y) Raman excitations in the 200–2800 cm-1 range as a function of temperature. Combinations of phonon energies are observed up to the fourth order, indicating the presence
of electron-phonon coupling. In comparison to Γ-point phonon combinations, double phonon excitations appear to be blue shifted
in large size rare earth ion compounds. The phonon combination intensities decrease rapidly with their increasing order, confirming
other studies which conclude that the electron-phonon coupling is not as strong as supposed in the localized limit. Moreover,
different intensity order dependences are observed between the phonon combination and the so-called Jahn-Teller mode. These
effects are better described in the orbiton-phonon coupling scheme. 相似文献
5.
Alexander N. Titov Ingrid Bryntse Svetlana G. Titova Nadezhda V. Toporova 《Solid State Ionics》2001,140(3-4):293-300
The reaction between metallic Ag and PbS1.18(TiS2)n, n=1, 2, misfit layer compounds has been investigated by electrochemical technique, X-ray powder analysis and transmission electron microscopy. It was found that silver intercalation is possible only in the compound with n=2. The thermodynamic behavior and location of phase boundaries were studied in the temperature range 400–650 K. DC-conductivity and magnetic-susceptibility measurements were performed, and the data can be interpreted as an appearance of small polarons during silver insertion. 相似文献
6.
C. Grimaldi L. Pietronero M. Scattoni 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):247-255
In the theory of nonadiabatic superconductivity several features are governed by the electron-phonon vertex correction which
has a complex structure both in momentum and frequency. We derive a physical interpretation of such nonadiabatic effects that
permits to link them to specific material properties. We show how the nonadiabatic vertex correction can be decomposed into
two terms with different physical origins. In particular, the first term describes the lattice polarization induced by the
electrons and it is essentially a single-electron process whereas the second term is governed by the particle-hole excitations
due to the exchange part of the phonon-mediated electron-electron interaction. We show that by weakening the influence of
the exchange interaction the vertex takes mostly positive values giving rise to an enhanced effective coupling in the scattering
with phonons. This weakening of the exchange interaction can be obtained by lowering the density of the electrons, or by considering
only long-ranged (small q) electron-phonon couplings.
Received 23 November 1998 and Received in final form 22 January 1999 相似文献
7.
J. El Khamkhami E. Feddi E. Assaid F. Dujardin B. Stbe M. El Haouari 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):366-373
The effect of a magnetic field on the ground-state energy of a donor impurity confined in a polar CdSe spherical quantum dot embedded in a nonpolar matrix is studied theoretically. The interaction between the all charge carriers (electron and ion) and the confined longitudinal optical phonons (LO-phonons) is taken into account by considering the strong coupling method (Landau–Pekar approach). A variational calculation is performed in the framework of the effective mass approximation using a trial wave function deduced from the second-order perturbation and assuming that the quantum dot has a finite depth potential. 相似文献
8.
L. Proville S. Aubry 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):405-421
We study the effective mass of the bipolarons and essentially the possibility to get both light and strongly bound bipolarons
in the Holstein-Hubbard model and some variations in the vicinity of the adiabatic limit. Several approaches to investigate
the quantum mobility of polarons and bipolarons are proposed for this model. First, the quantum fluctuations are treated as
perturbations of the mean-field (or adiabatic) approximation of the electron-phonon coupling in order to calculate the bipolaron
bands. It is found that the bipolaron mass generally remains very large except in the vicinity of the triple point of the
phase diagram (see [1]), where the bipolarons have several degenerate configurations at the adiabatic limit (single site (S0),
two sites (S1) and quadrisinglet (QS)), while the polarons are much lighter. This degeneracy reduces the bipolaron mass significantly.
Next we improve this result by variational methods (modified Toyozawa Exponential Ansatz or TEA) valid for larger quantum
perturbations away from the adiabatic limit. We first test this new method for the single polaron. We find that the triple
point of the phase diagram is washed out by the lattice quantum fluctuations which thus suppress the light bipolarons. Further
improvements of the method by hybridization of several TEA states do not change this conclusion. Next we show that some model
variations, for example a phonon dispersion may increase the stability of the (QS) bipolaron against the quantum lattice fluctuations.
We show that the triple point of the phase diagram may be stable to quantum lattice fluctuations and a very sharp mass reduction
may occur, leading to bipolaron masses of the order of 100 bare electronic mass for realistic parameters. Thus we argue that
such very light bipolarons could condense as a superconducting state at relatively high temperature when their interactions
are not too large, that is, their density is small enough. This effect might be relevant for understanding the origin of the
high superconductivity of doped cuprates far enough from half filling.
Received 15 September 1999 相似文献
9.
X.-F. Pang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):415-428
The influence of a soliton on the properties of the M?ssbauer effect resulting from the gamma-active nuclei situated at lattice
sites in quasi-one-dimensional anharmonically organic molecular chains, in which the active nuclei emit gamma-photons, has
been theoretically studied by a quantum vibrational model. An expression for the gamma-radiated M?ssbauer transition probability
as a function of the temperature and non-linear interaction has been obtained. Finally we give some new properties of this
effect from numerical calculation in such a case, which present a way to experimentally confirm the soliton existence in molecular
crystals.
Received 9 April 1998 and Received in final form 11 December 1998 相似文献
10.
Optical properties of an interacting large polaron gas 总被引:1,自引:0,他引:1
V. Cataudella G. De Filippis G. Iadonisi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):17-22
The normal state conductivity, , of a system of interacting large polarons is calculated within the Random Phase approximation and some numerical results
are presented. The behaviour of the optical absorption as a function of the charge carrier density and of the temperature
is analyzed for different values of the electron-phonon coupling constant. It is shown that exhibits features similar to those observed in the infrared spectra of the cuprates.
Received 27 January 1999 相似文献