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.

Phenomenological description of the longitudinal vibrations of the quasi-one-dimensional solid PtCl: calculation of the valence defect frequencies

Abstract: The longitudinal vibrations of the PtCl linear chain and those of various valence defects are described by a one-dimensional model in a first-nearest-neighbour interaction approximation. The analysis is performed as a function of the K2/K1 ratio (K1 and K2 representing the PtClIV-Cl and PtII-Cl force constants, respectively), which is shown to play an important role in the vibrational characteristics of the defects while the infrared frequencies are not strongly dependent on a particular ratio. A coherent description of the frequencies of the modes of the perfect chain and those of the polaronic defects is obtained for K2/K1=0.3. For this ratio the electron polaron and the electron bipolaron give rise to one Raman-active mode while at least two are predicted for the other investigated defects. The shapes of the Raman bands associated with the electron and hole polarons are explained by the chlorine isotopic effect. The vibration associated with the electron bipolaron is predicted to be at about 210 cm-1 where a broad line grows upon photolysis. An elementary calculation based upon a Born-Mayer potential for short-range interactions, adjusted from the interionic distances, leads to force constants of the same magnitude as those adjusted from the experimental frequencies.

Electronic structure of oligoaniline doped by inorganic and organic acids

Abstract: The electronic structure of doped-oligoaniline with various dopants is investigated by means of DFT method. After doping by hydrochloric acid (HCl) and camphorsulfonic acid (HCSA), the alternation of bond-lengths is decreased and the co-planarity of adjacent aromatic rings is increased. The π-conjugating effect is increased in the electronic nature of Ph-N system because the electrons can be delocalized along the backbone of oligoaniline where the hydrogen bonds as a bridge transfer the electrons. The electronic structure of polaron and bipolaron conformation and their relative stability is discussed, indicating that the preferable conformation is dependant on various dopants. The calculation results reveal that there is a relatively stronger interaction between the organic dopant of HCSA and N atoms of PANI, and more charge transfer between PANI and HCSA is a reason for the fact that the conductivity of HCSA-doped PANI is higher than that of HCl-doped PANI. The doping mechanism is proposed based on the calculation results. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Bipolarons or Polaron Pairs in Conducting Polymers: Equilibrium and Kinetics* , **

Abstract: Equilibrium and kinetics are compared for conjugated polymers, supposing the charged states are either polarons (Ps) and bipolarons (BPs) or polarons and polaron pairs (PPs). For low concentrations equilibrium and kinetics are virtually indistinguishable. Both are essentially different for high concentrations due to the fact that the extension of the bipolaron is almost the same as that of one polaron whereas the polaron pair has the extension of two polarons. As a result, the polaron concentration, i.e. the spin concentration, shows for a system with bipolarons a maximum and decreases for continuing increase of the potential. This dependence corresponds to results of ESR spectroelectrochemistry. In contrast, for the system with PPs both P and PP concentrations saturate at high potentials. Thus, the PP model is only reasonable if an additional subsequent second oxidation step is possible. The kinetics of the formation and dissociation of PPs or BPs, is essentially the same for concentrations that can be achieved in accumulation layers in organic MOS devices. The estimated relaxation times point to the formation and dissociation of either BPs or PPs as processes that can either cause or influence hysteresis effects in polymeric MOS capacitors, which can be described by an interface charge, depending on the sweep direction in the capacitance-voltage measurements.

Interactions between Fermi polarons in monolayer WS2

Abstract: Abstract Interactions between quasiparticles are of fundamental importance and ultimately determine the macroscopic properties of quantum matter. A famous example is the phenomenon of superconductivity, which arises from attractive electron-electron interactions that are mediated by phonons or even other more exotic fluctuations in the material. Here we introduce mobile exciton impurities into a two-dimensional electron gas and investigate the interactions between the resulting Fermi polaron quasiparticles. We employ multi-dimensional coherent spectroscopy on monolayer WS 2 , which provides an ideal platform for determining the nature of polaron-polaron interactions due to the underlying trion fine structure and the valley specific optical selection rules. At low electron doping densities, we find that the dominant interactions are between polaron states that are dressed by the same Fermi sea. In the absence of bound polaron pairs (bipolarons), we show using a minimal microscopic model that these interactions originate from a phase-space filling effect, where excitons compete for the same electrons. We furthermore reveal the existence of a bipolaron bound state with remarkably large binding energy, involving excitons in different valleys cooperatively bound to the same electron. Our work lays the foundation for probing and understanding strong electron correlation effects in two-dimensional layered structures such as moiré superlattices.