Su Zhao-bin

Theory of Soliton Generation and Lattice Relaxation in Polyacetylene (I) General Formalism

This series of papers is devoted to the theory of soliton and polaron generation in polyacetylene by both radiative and non-radiative processes. In the first paper of this series a general formalism is presented which combines the Lattice relaxation approach for the multiphonon process developed by Huang and many others with the consistency condition in terms of the Bogoliubov-de Gennes equation and the gap equation. The exact adiabatic electron wave functions consistent with the different lattice symmetry breaking in the initial and final states are used to calculate the transition probability between these multi-electron states. The formalism presented is illustrated by deriving a general expression for the non-radiative decay rate using the steepest descent method in the case of strong coupling. The theory developed here can be applied to treating the quantum transitions between states of differnet symmetry breaking when the multi-electron background effect and the consistency condition are essential. The applications of the general formalism to polyacetylene and the comparison with numerical results and the recent experiments wi11 be given in the succeeding papers.

Quantum Fluctuation of the Order Parameter and the Optical Absorption in Polyacetyleneo

We study in this paper the effects of lattice quantum fluctuations upon the order parameter in the Peierls systems by using the Greens function technique. We start from the discrete Su-Schrieffer-Heeger model with quantized phonon field and derive a coupled system of equations for the order parameter and Greens functions. It turns out that the order parameter is reduced compared with the adiabatic value but the Peierls instability survives the quantum fluctuations in agreement with, Monte Carlo results. The band-to-band optical absorption coefficient of polyacetylene with lattice fluctuation being accounted for is also calculated and compared with the experimental data.

POSSIBLE COEXISTENCE OF ANTIFERROMAGNETISM AND SUPERCONDUCTIVITY IN THE HUBBARD MODEL

The Hubbard model in the nearly half-filled case was studied in the mean field approximation using the effective Hamiltonian approach. Both antiferromagnetic order parameter and condensation of singlet pairs were considered. In certain parameter range the coexistence of antiferromagnetism and superconductivity is energetically favorable. In this paper relations to the high temperature superconductivity and other theoretical approaches are discussed.

On Theory of the Statistical Generating Functional for the Order Parameter(I) — General Formalism

A theoretical scheme using closed time-path Greens functions is proposed to describe the quantum statistical properties of the order parameter in terms of a generating functional. The dynamic evolution, is generated by a driving source, while the statistical correlation by a fluctuation source. The statistical causality is shown to hold explicitly and to give rise to a number of important consequences. The problem of determining the quantum statistical properties for the order parameter is reduced to finding a solution of the functional equation for it.

On a Dynamic Theory of Quenched Random System

A dynamical theory for quenched random system is developed in the framework of CTPGF. In steady states the results obtained coincide with Chose following from the quenched average of the free energy. The order parameter , a matrix in general, becomes an integral part of the second order connected CTPGF. An equation to determine is derived from the Dyson-Schwinger equation in this formalism. Some general properties of the CTPGF in a quenched random system are discussed.

On Theory of the Statistical Generating Functional For the Order Parameter (II) —Density Matrix and the Field-Theoretical Structure of the Generating Functional

Several equivalent expressions for the generating functional of the order parameter are derived in this paper to elucidate how the statistical properties are incorporated in its field-theoretical structure. It is shown that in the process of determining the generating functional the dynamic evolution and the statistical information can be separated to a certain extent which facilitates solving the problem. The whole procedure is greatly simplified if the statistical correlation is Gaussian or a generalized fluctuation-dissipation theorem (FDT) holds. As an example, the Gaussian character of the thermal-equilibrium distribution is justified and the Matsubara technique along the imaginary time axis is extended to the real axis to provide a complete perturbation scheme for the closed time-path Greens functions (CTPGF).

On an Approximate Form of the Coupled Equations of the Order Parameter with the Weak Electromagnetic Field for the Ideal Superconductor

A simplified derivation of, the macroscopic electrodynamic equations of Umezawa, Mancini et al. for superconductors is given in the framework of the closed time path Greens functions (CTPGF) using generalized Ward-Takahashi identities. It is shown that the forms of the equations obtained are the same for both thermo-equilibrium and nonequilibrium stationary states provided the electromagnetic field is weak and its effect on the modulus of the order parameter can be neglected. The statistical behavior of the states is completely specified in the equations by parameters which can be calculated by the method of CTPGF.

On Theory of the Statistical Generating Functional for the Order Parameter (III) –Effective Action Formalism for the Order Parameter

A practical scheme is proposed in this paper to determine the quantum statistical properties of the order parameter in the frame work of the closed time-path Greens functions (CTPGF). As a microscopic quantum theory, this formalism is applicable in principle to both equilibrium and nonequilibrium phenomena and is capable of dealing with statistical systems both above and below their phase transition point. This formalism can be used to discuss the statistical properties of simple as well as composite order parameters in either uniform or nonuniform systems. As simple illustrations and check for the theory, the proposed prescription is applied to the contact-interaction model for superconductivity and a unimode laser system coupled with two-energy-level bound electrons.

RVB-Itinerant P Hole Model for High-Tc Copper Oxides

A model for the high-Tc Copper Oxides is studied. The localized nature of Cu 3d electrons is described as the RVB quantum spin liquid and the doped O 2p holes are described with an itinerant band. Our analysis shows that the virtual exchange of two spinons induces a pairing interaction between two holes.

Soliton and Polaron Dynamics in Conducting Polymers

Solitons and polarons in conducting polymers are strongly coupled electron-lattice excitations. The lattice relaxation theory generalized by us to include the self-consistency of multi-electron states with lattice symmetry-breaking is summarized. The discrete symmetries and corresponding selection rules for both radiative and nonradiative processes are discussed. Theoretically calculated probability of nonradiative decay of an electron-hole pair into a soliton pair and that of electron (hole) into polaron as well as the probability of soliton pair photo-generation is compared with results of numerical and laboratory experiments. The resonance Raman scattering data of cis-polyacetylene are interpreted in terms of a bipolaron model. The parameters involved are determined directly from experimental data. Other applications of lattice relaxation theory to conducting polymers are briefly mentioned.