High electrical conductivity in nonlinear model lattice crystals mediated by thermal excitation of solectrons

The quantum statistics of electrons interacting with nonlinear excitations of a classical heated nonlinear lattice of atoms is studied. By using tight-binding approximation, Wigner momentum distributions and computer simulations we show the existence of quite fast and nearly loss-free motions of charges along crystallographic axes and estimate the range of values of transport coefficients. Using minimization of free energy we estimate the density of mobile bound states between electrons and lattice solitons (so-called solectrons). We calculate the momenta of Wigner velocity distributions and from Kubo relations the diffusivity and the electrical conductivity using the relaxation time approximation. We show that thermally excited solectrons in nonlinear media may lead to a significant transport enhancement. Our estimates and computer simulations demonstrate the existence of a temperature window, where solectrons are relatively stable and contribute strongly to transport. The electrical conductivity may be enhanced up to two orders of magnitude.     

Head-on and head-off collisions of discrete breathers in two-dimensional anharmonic crystal lattices

The ground-state phase diagram of the extended Falicov-Kimball model with f-f electron hopping is studied numerically in the one-dimensional case. To identify the nature of ground states three complementary numerical methods are used, and namely, (i) the small-cluster exact-diagonalization method, (ii) the density-matrix-renormalization-group method (DMRG) and (iii) an approximate, but very accurate, numerical method based on the reduction of the Hilbert space. It is found that the physics of the Falicov-Kimball model found for the zero value of the f-electron hopping integral t _f (including the existence of the devil’s staircase structure) persists also at finite values of t _f . The critical values of t ^c _f below which the physics of the Falicov-Kimball model dominates are calculated numerically and it is shown that they depend very strongly on the f-electron concentration n _f and only very weakly on the Coulomb interaction. In particular, we have found that for strong Coulomb interactions the value of t ^c _f rapidly increases from t ^c _f ~ 0.003 found for n _f = 1 / 4 up to relatively large t ^c _f ~ 0.4 found for n _f near the half-filled band case n _f = 1 / 2. In addition, the complete picture of valence transitions is presented for non-zero t _f and strong Coulomb interactions.