Narrow Results

We investigate the effects of hole doping in the charge-density wave (CDW) state that has the strong electron-phonon (e-p) coupling, using the two-dimensional molecular crystal model. In calculations, we use the mean-filed theory for the interelectronic interactions and the adiabatic approximation for phonons. On the basis of this theory, we calculate e-p states of doped ground states for various values of the doping concentration of holes. Prom the calculated results, it is found that a multistable nature appears in the doped e-p states just before the CDW-metal phase transition. In order to see the effects of the photoexcitation in the hole-doped states, we also investigate the exciton states taking into account the electron-hole correlation. Results calculated here indicate that the separation of electron and hole occurs in the photoexcited states as a consequence of the energy relaxation of excitons.

The multistability problem is studied for the complex-valued Cohen-Grossberg neural networks (CVCGNNs) with unbounded time-varying delays. By using the fixed point theorem and other analytical tools, some novel algebraic criteria are established to guarantee that the existence of equilibrium points and μ-stability of the CVCGNNs. The obtained results generalize some previous works in the literature. Finally, one numerical example is presented to show the validity of the theoretical results.