Topic
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.
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01 Jan 1985
TL;DR: In this article, the authors tried to get information on the electronic structure of conducting polymers by electron energy-loss spectroscopy (ELS) and investigated polyparaphenylene (PPP), polypyrrole (PPY) based polymers, and polythiophene (PT) with various counterions.
Abstract: For the understanding of the macroscopic properties of conducting polymers (e.g., the high conductivity) the knowledge of the evolution of the π-electron bandstructure as a function of doping concentration is of fundamental importance. We have tried to get information on the electronic structure of conducting polymers by electron energy-loss spectroscopy (ELS). In particular, we have investigated polyparaphenylene (PPP), polypyrrole (PPY) based polymers, and polythiophene (PT) with various counterions. These polymers have the common feature of a non-degenerate ground state; namely, when the positions of the double and single bonds are reversed, an inequivalent structure with different energy results. Theoretical calculations [1–4] have predicted that polarons,and at higher concentrations bipolarons,are the primary defect states created during doping of conjugated polymers with non-degenerate ground states. This leads to two defect states in the gap, the lower one being singly occupied in the polaron case for p-doping. Further oxidation leads to bipolarons with two empty (occupied) states in the gap for p(n) doping. At higher doping level, a broadening of the defect level is predicted and at the highest doping level, an overlap of the bipolaron bands with the π bands should occur,leading to a partially filled valence (conduction) band for p(n) doping. The defect levels,as well as the overlap of bipolaron bands with the π bands,should be observable by optical spectroscopy or by ELS.
1 citations
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TL;DR: In this article, the phase diagram of halogen-bridged mixed-valent metal complexes was studied using a two-band extended Peierls-Hubbard model employing the recently developed Density Matrix Renormalization Group method.
Abstract: The phase diagram of halogen-bridged mixed-valent metal complexes ($MX$) has been studied using a two-band extended Peierls-Hubbard model employing the recently developed Density Matrix Renormalization Group method. We present the energies, charge and spin density distributions, bond orders, charge-charge and spin-spin correlations, in the ground state for different parameters of the model. The effect of bond alternation and site-diagonal distortion on the ground state properties are considered in detail. We observe that the site-diagonal distortion plays a significant role in deciding the nature of the ground state of the system. We find that while the $CDW$ and $BOW$ phases can coexist, the $CDW$ and $SDW$ phases are exclusive in most of the cases. We have also studied the doped $MX$ chains both with and without bond alternation and site-diagonal distortion in the $CDW$ as well as $SDW$ regimes. We find that the additional charge in the polarons and bipolarons for hole doping are confined to a few sites, in the presence of bond alternation and site-diagonal distortion. For electron doping, we find that the additional charge(s) is(are) smeared over the entire chain length and although energetics imply a disproportionation of the negatively charged bipolaron, the charge and spin density distributions do not reflect it. Positively charged bipolaron disproportionates into two polarons in the $SDW$ region. There is also bond order evidence for compression of bond length for the positively charged polaronic and bipolaronic systems and an elongation of the bonds for systems with negatively charged polarons and bipolarons.
1 citations
TL;DR: In this article, it was shown that the magnetic bipolaron can be formed if the distance between two polarons is less than some critical value, i.e., the larger the lower the dimensionality of the system, lower the temperature, and larger the single-polaron radius.
Abstract: Interaction of two magnetic polarons formed either by single carriers or by excitons is considered in bulk crystal, quantum well and quantum wire. It is shown that the magnetic bipolaron can be formed if the distance between two polarons is less than some critical value. This critical radius is the larger the lower the dimensionality of the system, the lower the temperature and the larger the single-polaron radius. The critical distance for the neutral-magnetic-bipolaron formation is much longer than for the charged bipolaron.
1 citations
TL;DR: In this paper, a conformation change in the molecular structure, such as a difference in the torsion angle between neighboring thiophene rings due to the introduction of vinylene groups, is discussed in terms of polaron and/or bipolaron model.
1 citations
TL;DR: In this article, a simple Hamiltonian for poly(p-phenylene) in the framework of SSH tight binding model was proposed, which showed that the formation of doubly charged bipolaron is energetically more favorable than the-formation of two polarons with single, charge.
Abstract: We have proposed a simple Hamiltonian for poly(p-phenylene) in the framework of SSH tight binding model. The calculations presented to the ground state, polaron and bipolaron show that the formation of doubly charged bipolaron is energetically more favorable than the-formation of two polarons with single, charge. Because the period of the chain is 4a, the CB and VB band will split in two, and when there is a polaron (or bipolaron) in the chain, shallow energe levels will emerge near each band edge besides the polaron (or bipolaron) energe levels, all the corresponding electronic states are localized.
1 citations