Bipolaron

About: Bipolaron is a research topic. Over the lifetime, 1335 publications have been published within this topic receiving 29154 citations. The topic is also known as: bipolarons.

In situ optical absorption spectra and electron spin resonance measurements of poly(1,4-naphthalene vinylene) during electrochemical n-type doping

Abstract: The electrochemical, optical and magnetic properties in poly(1,4-naphthalene vinylene) (PNV) during electrochemical n-type doping have been investigated by cyclic voltammetry, optical absorption spectroscopy, and electron spin resonance (ESR) measurements. Evidence for electrochemical n-type doping of this polymer and evolution of localized states is obtained from measurements of a cyclic voltammogram and is demonstrated by the spectral change associated with doping. In the lightly doped state only two absortpion peaks originating from the transitions between two gap states and the conduction band appear within the gap region at 1.1 and 1.7 eV. The spin susceptibility increases by about two orders of magnitude from 5.9*10-8 to 6.1*10-6 emu mol-1 upon doping up to a dopant concentration of about 2.8 mol.%. With a further increase in dopant concentration the spin susceptibility decreases slightly. The spin density evaluated from the susceptibility was inconsistent with the polaron density assumed to be formed by dopants of 2.8 mol.%. That is, even at lightly doped slates the newly developed species turn into n-type spinless bipolarons. The ESR linewidth decreases by doping from about 9.9 G to 0.4 G. The g factor of 2.0031 at the neutral state shifts upon doping to the smaller value 2.0028, which corresponds to the nearly free electron g factor. These results are discussed in terms of bipolaron models.

Stability of bipolarons, electron-electron correlations, the variational principle, and the virial theorem

Abstract: For bipolaron states, a relation is established between the variational principle and the virial theorem optimizing the electronic wave functions. It is shown that a bipolaron one-center state is unstable under any conditions that do not violate basic physical principles. It is established that a stage-by-stage increase in the flexibility of the electronic wave function due to the electron-electron correlations does not stabilize a one-center bipolaron. It is argued that the results of calculations based on the one-center bipolaron model are incorrect.

Vibronic bipolaron model for the high-Tc superconductivity

Abstract: An alternative type of small polaron associated with an off-center configurational distortion can arise from the additional coupling of the electron to some appropriate odd vibrational mode. The off-center polaron is inherently polarizable in an electric field. Consequently, neighboring entities can couple through the universal Van der Waals force to form bipolarons. Implications for the high-T c superconductivity are discussed, bipolarons in superconducting cuprates being envisaged as asymmetric Cu O central-cage linear chains.

Polaronic excitations in the doped polyacene

Abstract: The polyacene as two coupled chains of transpolyacetylene has been studied based on an extended SSHHubbard model. The dimerized displacement u0 is found to be similar to the case of trans-polyacetylene, and equals to 0.04 A. The energy-band gap is 0.38 eV, in agreement with other authors. In particular, we have considered some cases where polyacene is doped with one and two donor electrons. In the case of doping with one electron, a polaron spreading over two chains has been found; in the case of doping with two electrons having different spins, a stable bipolaron has been obtained, which is different from the one of transpolyacetylene; in the case of doping with two electrons having the same spins, two stable polarons which spread over two chains have been found. The bound electronic states corresponding to these cases are obtained.

Bipolaron Formation and Nonlinear Optical Properties in Bis-Thienyl Polyenes

Abstract: Bipolaron-like dications have been produced in both diphenyl and bis-thienyl polyenes by oxidative doping in solution. However, until now spectroscopie studies of the charge state generation beyond the hexaene have been precluded due to lack of solubility and processibility. We have now been able to extend these studies to the decaene by incorporating solubilizing substituents on the thienyl end caps. For the neutral species, degenerate four wave Mixing (DFWM) studies indicate that χ (3) is still increasing as a function of conjugation length. Introduction of mesomerically interactive RS groups on the thiophene rings further increases both solubility and optical nonlinearity.