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 $\chi$ and to the specific heat $C$ of a metal. The impurity contribution to the magnetic susceptibility has a $1/T^2$ behaviour, and the impurity contribution to the specific heat has a $1/T$ behaviour, both in an extended region of temperatures $T$. 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 $C$ and $\chi$ 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 $[Pt(en)_2][Pt(en)_2 Cl_2](ClO_4)_4$(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 $E_{low}(k)$ of one-dimensional half-integer spin generalized Heisenberg models and half-filled extended Hubbard models are $\pi$-periodic functions. For Hubbard models at fractional fillings $E_{low}{(k+ 2 k_f)} = E_{low}(k)$, where $2 k_f= \pi n$, and $n$ 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 $E_{low}(k) = 0$ for any $k$, 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