69 research outputs found
Interaction of discrete breathers with electrons in nonlinear lattices
We study the effects of electron-lattice interaction in the presence of
discrete breathers. The lattice is treated classically. We consider two
different situations - i) the scattering of an electron by a discrete breather
in the semiconducting regime, where the electron-breather distance is large
compared to the breather size, and ii) the appearance of a bound
electron-breather state, which exists at least over one half of the breather
period of oscillation. In the second case the localization length of the
electron can be of the order of the breather size - a few lattice periods.
Remarkably these results are derived in the absence of disorder, since discrete
breathers exist in translationally invariant nonlinear lattices
Quasiclassical Hamiltonians for large-spin systems
We propose a method for obtaining effective classical Hamiltonians \cal H for
many-body quantum spin systems with large spins. This method uses the
coherent-state representation of the partition function Z and the cumulant
expansion in powers of 1/S. For the quantum Hamiltonian \hat H of a Heisenberg
form, the 1/S corrections in \cal H have a non-Heisenberg many-spin form. The
effective Hamiltonian \cal H can be treated by methods familiar for classical
systems. The non-Heisenberg terms in \cal H may be responsible for such effects
as spin-Peierls transition and uplifting of the classical degeneracy by quantum
fluctuations.Comment: 8 Pages, 2 Figures, submitted to EPJ
On the ground state of solids with strong electron correlations
We formulate the calculation of the ground-state wavefunction and energy of a
system of strongly correlated electrons in terms of scattering matrices. A
hierarchy of approximations is introduced which results in an incremental
expansion of the energy. The present approach generalizes previous work
designed for weakly correlated electronic systems.Comment: 17 pages, Latex(revtex
Nuclear magnetic susceptibility of metals with magnetic impurities
We consider the contribution of magnetic impurities to the nuclear magnetic
susceptibility and to the specific heat of a metal. The impurity
contribution to the magnetic susceptibility has a behaviour, and the
impurity contribution to the specific heat has a behaviour, both in an
extended region of temperatures . In the case of a dirty metal the RKKY
interaction of nuclear spins and impurity spins is suppressed for low
temperatures and the main contribution to and is given by their
dipole-dipole interaction.Comment: 9 pages, 4 figures, REVTE
Intrinsic localized modes in the charge-transfer solid PtCl
We report a theoretical analysis of intrinsic localized modes in a
quasi-one-dimensional charge-transfer-solid (PtCl). We discuss strongly nonlinear features of resonant Raman
overtone scattering measurements on PtCl, arising from quantum intrinsic
localized (multiphonon) modes (ILMs) and ILM-plus-phonon states. We show, that
Raman scattering data displays clear signs of a non-thermalization of lattice
degrees-of-freedom, manifested in a nonequilibrium density of intrinsic
localized modes.Comment: 4 pages, 4 figures, REVTE
On the lowest energy excitations of one-dimensional strongly correlated electrons
It is proven that the lowest excitations of one-dimensional
half-integer spin generalized Heisenberg models and half-filled extended
Hubbard models are -periodic functions. For Hubbard models at fractional
fillings , where , and is
the number of electrons per unit cell. Moreover, if one of the ground states of
the system is magnetic in the thermodynamic limit, then for
any , so the spectrum is gapless at any wave vector. The last statement is
true for any integer or half-integer value of the spin.Comment: 6 Pages, Revtex, final versio
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