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.

Photoreflectance of reduced poly 3‐methyl thiophene

Abstract: We present photoreflectance studies of poly 3‐methyl thiophene as a function of doping level, temperature, and light intensity. The as‐grown polymer does not show any photoreflectance signal. As the doping level is reduced by electrochemical reduction of the polymer, two peaks are observed in the spectra. One peak, at ∼2 eV, corresponds to the band‐to‐band transition. The second peak, at ∼1.7 eV, corresponds to the transition between the top of the valence band and the upper bipolaron level. These results are almost identical to those reported for the electrolyte electroreflectance of the polymer when it was in contact with an aqueous electrolyte. The major difference in the results using these two techniques is in the observation, in photoreflectance, of the bipolaron transition in the neutral, fully reduced polymer. This was interpreted in terms of bipolaron formation through photodoping. The similar spectral characteristics between the photodoped and electrodoped bipolaron are further support to the fi...

Large Bipolarons in Two and Three Dimensions

Abstract: The large bipolaron in two and three dimensions is investigated by combining the reasonable asymptotic relative wavefunctions and the Lee–Low–Pines–Huybrechts (LLP-H) variational method. The values of the critical coupling constant above which bipolarons may exist and the critical ratio of dielectric constants below which bipolarons may exist are evaluated, which are very close to the recent results obtained within totally different variational approaches. It is also found that low-dimensional materials are more favorable for the formation of bipolarons.

Band Structure Calculations for the Polaron Lattice in the Highly Doped Regime of Polyacetylene, Polythiophene, and Polyaniline

Abstract: Band structure calculations are presented for the polaron lattice conformation in the highly doped regime of polyacetylene, polythiophene, and polyemeraldine. We have also performed calculations for the soliton lattice in polyacetylene and for the bipolaron lattice in polythiophene and polyemeraldine. The polaron lattice band structures are found to be in good agreement with the observed optical absorption and magnetic data for the three polymers which all exhibit a metallic-like behavior in their highly doped state. The polaron lattice band structures for polyacetylene and polythiophene are calculated to be very similar, which is consistent with the experimental trends. The polyemeraldine salt bipolaron and polaron band structures present a single defect band deep in the gap, instead of the two defect bands usually found in other conjugated systems. This peculiarity is related to the lack of electron-hole symmetry in polyaniline and leads to a modified picture for the electronic transitions appe...

Mobile Bipolaron—Strong Coupling Approach

Abstract: We explore the properties of the bipolaron in a 1D Holstein-Hubbard model with dynamical quantum phonons. We apply strong coupling theory to investigate the intersite bipolaron. We investigate the influence of the Hubbard interaction on the bipolaron binding energy, effective mass, and phase diagram. We compare our analytic results to recent numerical calculations [1]. In the intermediate and strong coupling regimes, a bipolaron is stable beyond the naive stability limit U 0 = 2ωg 2 . The intersite bipolaron has a significantly reduced mass compared to the single site bipolaron, and is stable in the strong coupling regime up to U c ∼ 4ωg 2 .