171 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
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