We study solitonic charge transport in a hydrogen-bonded model system representing a one-dimensional polypeptide chain. Supersonic solitons are constructed for zero temperature in the frame of a Morse lattice model for which an ͑nonlinear͒ electronic system is coupled in a tight-binding approximation to H-bond vibrations of the molecular chain. The latter are of anharmonic nature. Charge transport is realized via the coupling between the electron and the local lattice deformations. This electron-lattice coupling is described by the soliton solutions, assigned to states of a localized charge in association with its local chain deformation. By retaining the discrete nature of the underlying lattice system it is shown that even strongly localized states are mobile. In fact, we illustrate that for nonlinear electron-vibration interaction supersonic solitonic carriers in the lattice assist the transport of narrow electron and lattice solitons. Moreover, by using realistic values from polypeptides for the system parameters we demonstrate that the interaction between the H-bond vibrations and the electron is strong enough to sustain thermal perturbations up to T = 300 K. Most importantly localization is maintained over extended periods of time during which the electron travels directionally over such long distances along the chain exceeding by far those achievable with single-step tunneling. Furthermore, we discuss the role of an applied electric field. It is demonstrated that in a wide range of its values the velocity of the soliton motion and hence the electric current remains unaffected by the electric field. Above this range the velocity of the solitons is proportional to the field strength so that the corresponding current follows Ohm's law. Then for still higher field strengths above a critical value the coupling between electron and soliton dynamics breaks down.

We study electron-electron pairing in an one-dimensional model lattice system embedded into a three-dimensional environment. The electron pair potential is lowered by a single, localized lattice deformation. Such a deformation is related to solitons moving along the lattice. Yet the exact form and the time evolution of the lattice excitation are of secondary relevance as the electron pair is stable for sufficiently wide deformations which propagate on molecular time scales, e.g. velocity of sound electron velocity. The spatial structure of the pair potential and the electron-electron wave function bring a mechanism of pairing different from the exchange of phonons between the electrons and the lattice which leads to Cooper pairs, and different also from the formation of bipolarons.

Assuming the quantum mechanical "tight binding" of an electron to a nonlinear lattice with Morse potential interactions we show how electric conduction can be mediated by solitons. For relatively high values of an applied electric field the current follows Ohm's law. As the field strength is lowered the current takes a finite, constant, field-independent value.

Key words Dense plasmas, dielectric function, dynamic structure factor, Mott effect, metal-nonmetal transition. PACS 52.25Mq, 52.27Gr, 52.27Lw, 52.38DxLinear response theory is used to describe the response of a charged particle system to external electromagnetic fields. Properties such as the polarization function, the dynamical conductivity and the absorption coefficient are expressed in terms of equilibrium correlation functions. Many-particle theory is used to treat correlations in the Coulomb system. The systematic inclusion of bound states is shown. Modifications due to the influence of a dense medium lead to the dissolution (Mott effect) of bound states, which is adequately described in terms of the single-particle spectral function.

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