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.

Polaron-bipolaron—soliton doping in polyacetylene

Abstract: We have performed a self-consistent numerical study, which allows each CH group in a finite polyacetylene chain to relax to its equilibrium position, in order to investigate the formation of the polaron, soliton, and soliton lattice in the framework of Su-Schrieffer-Heeger model. The bondalternation order parameter, the delocalization of the gap states, the polaron-formation energy, the soliton-formation energy, the Peierls gap, and the gap separating the valence (or condition) band and the impurity band are calculated as functions of dopant level. The effect of electron-electron interaction is then examined in the Hartree approximation. Our results are compared with those derived by other authors. Although our approach simulates a doping process, further calculation based on the decaying of an electron-hole pair into a soliton-antisoliton pair gives exactly the same results as those shown in this paper. In particular, our finding clearly demonstrates the singlecharge injection via polarons which subsequently combine to form soliton-antisoliton pairs, in agreement with the recent experimental discovery.

Bipolarons and multipolarons consisting of impurity atoms in a Bose-Einstein condensate

Abstract: The variational Feynman formalism for the polaron, extended to an all-coupling treatment of bipolarons, is applied for two impurity atoms in a Bose-Einstein condensate. This shows that if the polaronic coupling strength is large enough, the impurities will form a bound state (the bipolaron). As a function of the mutual repulsion between the impurities, two types of bipolaron are distinguished: a tightly bound bipolaron at weak repulsion and a dumbbell bipolaron at strong repulsion. Apart from the binding energy, the evolution of the bipolaron radius and its effective mass are also examined as a function of the strength of the repulsive interaction between the impurities and of the polaronic coupling strength. We then apply the strong-coupling formalism to multiple-impurity atoms in a condensate, which leads to the prediction of multipolaron formation in the strong-coupling regime. The results of the two formalisms are compared for two impurities in a condensate, which results in a general qualitative agreement and a quantitative agreement at strong coupling. Typically, the system of impurity atoms in a Bose-Einstein condensate is expected to exhibit the polaronic weak-coupling regime. However, the polaronic coupling strength is, in principle, tunable with a Feshbach resonance.