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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TL;DR: In this paper, the authors used the continuous-time random-walk approximation based on CBH to estimate the density of charged defects and applied it to experimental data for amorphous As2Se3.
Abstract: Although the pair approximation (PA) based on correlated bamer hopping (CBH) is now fairly well established to explain the a.c. conductivity of amorphous chalcogenides, the density of charged states deduced from PA is large compared with those estimated from other studies, namely light-induced electron spin resonance and drift mobility. We have used the continuous-time random-walk approximation based on CBH to estimate the density of charged defects and have applied it to experimental data for amorphous As2Se3, and a density of charged defects consistent with other measurements has been estimated.
4 citations
TL;DR: In this paper, the electronic properties and electron correlations of the bipolaron formed by the electron-hole excitations in the presence of Yukawa-type coupling (between nonrelativistic fermions) in three spatial dimensions were investigated.
Abstract: We investigate the electronic properties and electron correlations of the bipolaron formed by the electron-hole excitations in the presence of Yukawa-type coupling (between nonrelativistic fermions) in three spatial dimension. The electron-hole excitation, which is necessary to the formation of bipolaron, leads to imaginary particle-hole order parameter, and provide finite boson field mass to the single-polaron dispersion in a broken-symmetry phase. We found that the bipolaron exhibits fermi-liquid features as long as the long-range strong interaction is suppressed, and it behave differently compared to the single-polaron. The bosonic momentum determines the mass of boson field propagator and the gap function, and it also related to the self-energies and the single-particle Green's functions. The Thouless criterion is also used during the calculation of gap equation at critical temperature (which become lower in weak-coupling regime), which corresponds to the pole (instability) of the pair propagator in zero center-of-mass freamwork. The mean field term and the bosonic fluctuation-induced contribution to free energy of bipolaron are also studied.
4 citations
TL;DR: In this paper, an effective polaronic Hubbard model is derived, where squeezing effects are taken into account, and correlations are treated in the slave-boson saddle-point approximation.
Abstract: The polaron formation at finite densities is studied in the Holstein-Hubbard model transformed, by a modified Lang-Firsov transformation, to a polaron Hamiltonian. In a variational approach, an effective polaronic Hubbard model is derived, where squeezing effects are taken into account. The correlations are treated in the slave-boson saddle-point approximation. Including charge- and magnetically ordered states the phase diagram is calculated, and a self-trapping transition from light to heavy polarons is found. The optical conductivity of heavy polarons reveals correlation-induced structures. By a Schrieffer-Wolff transformation up to second order in the residual polaron-multiphonon interaction, an effective polaron model is derived, where for a polaronic attraction an on-site bipolaron model is obtained.
4 citations
TL;DR: In this paper, the authors investigated the geometries and optical transitions of phenylene-based organic materials in pristine and doped states, paying special attention to chain-length effects as well as to the implications of inter-ring twists considering also bridged ladder type molecules.
4 citations
TL;DR: In this article, a broad band impedance spectroscopy (BSIS) was used to detect single and bipolaron hopping in chalcogenide glasses and its interdependencies on thermal history of the glass samples.
Abstract: We report direct evidence for the characteristic behavior of single and bipolarons in chalcogenide glasses by using broad band impedance spectroscopy. The measured ac conductivity, σ(f, T) of Te based glasses exhibit distinct behavior from those reported in amorphous tetrahedral semiconductors depending on the temperature and frequency. At low temperatures, the measured conductivity is exclusively due to the bipolarons between two charged defect centers. On the other hand, at high temperatures we find in addition to bipolaronic contribution, the single polaron hopping between a charged and neutral defect centers. The behavior of both types of charge carrier (single and bipolaron) shows the distinct relaxation characteristics within the measured frequency window. Remarkably, we observe existence of neutral defect centers with large concentration in tellurium-based chalcogenide glass under dark (normal) conditions revealed by the electron spin resonance (ESR) spectroscopy, which is an essential component for the single polaron hopping process. The estimated neutral defect centers from the dc conductivity measurements are in agreement with those derived from the ESR results. Further, we found that the effective correlation energy (Ueff) becomes less negative in glasses which exhibit single polaron hopping than the glasses found to exhibit typical bipolaronic conduction. The present work unequivocally demonstrates the characteristic behavior of single and bipolarons in chalcogenide glasses and its interdependence on thermal history of the glass samples.
4 citations