M. J. Rice

Charged Π-phase kinks in lightly doped polyacetylene

Abstract If polyacetylene is viewed as a Peierls-distorted linear chain it is concluded that extra electrons or holes added to polyacetylene via light doping will be accomodated in polyacetylene in the form of charged π-phase kinks, rather than filling available electron band states.

Towards the experimental determination of the fundamental microscopic parameters of organic ion-radical compounds

Abstract The electron transfer integral t, the on-site Coulomb repulsion U and the linear electron-molecular vibration (EMV) coupling constants {gα} are microscopic parameters fundamental in the understanding of the physical properties of organic ion-radical compounds. For those compounds in which the ion-radical molecules are present as quasi-isolated dimers, we demonstrate that all of these parameters may be measured via polarized optical reflectance. The role of U in suppressing the EMV coupling is stressed.

Phase phonons and intramolecular electron-phonon coupling in the organic linear chain semiconductor TEA(TCNQ)2

Abstract The vibrational excitations responsible for the remarkable series of infrared absorption bands observed in the organic linear chain semiconductor TEA(TCNQ)2 are identified to be the phase phonons which result from the coupling of the conduction electron molecular orbital to the totally symmetric vibrations of the TCNQ molecule.

Intramolecular vibrational stabilization of the charge density wave state in organic metals

Abstract On the basis of a tight-binding molecular orbital model of a conducting chain of large planar organic molecules we conclude that the charge density wave state in the organic metal TTF-TCNQ is stabilized predominantly by a set of small amplitude intra molecular distortions while the condensate effective mass characterizing its dynamical properties is dominated by large amplitude inter molecular distortions.

Electron-phonon coupling in intrinsic trans-polyacetylene

Abstract We consider a valence force field model for the phonon spectrum of (CH) x and find that phonon coupling to extended π electron states must be included to describe the observed Raman active modes of the polymer. The calculated phonon spectra are shown to possess the zone center dispersion anomalies characteristic of a condensed Peierls ground state.

Transition to a gapless Peierls insulator in heavily-doped polyacetylene

Abstract A high doping concentrations, polyacetylene undergoes a transformation into a state characterized by high d.c. conductivity, by a large Pauli susceptibility and by the absence of the interband transition of the updoped polymer. The optical spectrum shows a pseudogap at ≈0.2 eV and vibrational modes which imply that the carbon-carbon bond length is not uniform. We conclude that this state is best described as a gapless incommensurate Peierls insulator.

Phenomenological theory of soliton formation in lightly-doped polyacetylene

Abstract A phenomenological theory is introduced to investigate the influence on soliton formation of the Coulomb repulsion associated with the double occupation of the solitons localized mid-gap state and the solitons interaction with the iodized dopant molecule. Markedly different equilibrium parameters result for the neutral, charged-free and charged-pinned soliton forms. The frequency of the i.r. active pinning mode is predicted to be of the order of 300 cm -1 . A large zero-point motion is found for shape deformations of the soliton.

Insulator-to-metal transition in doped polyacetylene

Abstract A field-theoretic model of the insulator-to-metal transition in doped polyacetylene is presented. The likelihood of an inhomogeneous distribution of charge in the (CH)x fibrils is stressed.

Dynamical properties of the Peierls-Fröhlich state on the many-phonon-coupling model

Abstract The amplitude and phase phonons and the frequency dependent conductivity below the mean-field Peierls-Frohlich transition temperature T c , and the Kohn anomaly and fluctuation induced charge-density-wave conductivity above T c , are discussed on the basis of the many-phonon-coupling model recently introduced by Rice, Duke and Lipari. For dominant intramolecular phonon coupling an isotope effect in T c is related to the isotopic shift in the small polaron binding energy.

Electron-hole collision cross section in discrete hopping systems

Abstract Electron-hole collisions mediated by their Coulomb attraction are simulated for discrete hopping systems in the presence of a high electric field E . The collision cross section S is found to be field-dependent and sensitive to transport anisotropy. For microscopically isotropic systems S is well represented by S E = 4 πe / ϵE , following from the Langevin recombination theory. For anisotropic systems it is demonstrated that S can be much larger or smaller than S E for current flow along the direction with the smaller or larger mobility, respectively. This effect is found to arise even in nominally isotropic systems because of the field-induced mobility anisotropy. Disorder, however, tends effectively to decrease the apparent degree of anisotropy.