Collective excitation spectra of one-dimensional electron systems

Boosting the Seebeck Coefficient for Organic Coordination Polymers: Role of Doping-Induced Polaron Band Formation

Organic polymers are becoming emerging thermoelectric materials. Tremendous progress has been achieved for p-type doping, but efficient n-type organic materials are still rare. By investigating potassium-doped n-type poly(nickel-ethylenetetrathiolate) using density functional theory coupled with Boltzmann transport equation, we find that (i) formation of the electron polaron band (EPB) split from the conduction band (CB) dominates electron transport; (ii) at low doping concentration, the upper CB gets involved in transport in addition to the EPB as the temperature rises, leading to a highly elevated Seebeck coefficient and power factor; and (iii) at even higher temperature, because the CB starts to dominate, the Seebeck coefficient levels off and then decreases with temperature. Such an "exotic" nonmonotonic temperature effect has been found in experiment but has never been explained. We find that such behavior is primarily due to a polaron effect. A doping-induced polaron band can be employed to boost the Seebeck coefficient, making the organic coordination polymer a peculiar n-type thermoelectric material.

Nonlinear electromagnetic response of a uniform electron gas

The linear electromagnetic response of a uniform electron gas to a longitudinal electric field is determined, within the self-consistent-field theory, by the linear polarizability and the Lindhard dielectric function. Using the same approach, we derive analytical expressions for the second- and third-order nonlinear polarizabilities of the three-, two-, and one-dimensional homogeneous electron gases with the parabolic electron energy dispersion. The results are valid both for degenerate (Fermi) and nondegenerate (Boltzmann) electron gases. A resonant enhancement of the second- and third-harmonics generation due to a combination of the single-particle and collective (plasma) resonances is predicted.

Confinement and correlation effects on plasmons in an atom-scale metallic wire

We have studied the effect of confinement and correlations on the plasmon dispersion in an atom-scale metallic wire by determining the electron density response function. The wire electrons are modelled as comprising a quasi-one-dimensional homogeneous gas, with different transverse confinement models. The response function is calculated by including electron correlations beyond the random-phase approximation within the self-consistent mean-field approach of Singwi et al (1968 Phys. Rev. 176 589). The plasmon dispersion results are found to be in very good agreement with the recent electron-energy-loss spectroscopy measurements by Nagao et al (2006 Phys. Rev. Lett. 97 116802). However, our predictions are found to depend strongly on the nature of the confinement model, the structure of the one-dimensional electronic band and the electron effective mass, implying a crucial role for the wire structure.