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.

Translation invariance and the problem of the bipolaron

Abstract: Differences between translation-invariant and broken-symmetry bipolaron theories are analyzed in detail. It is shown that the Bogolyubov?Tyablikov canonical transformation allows collective coordinates to be introduced in a regular way for two particles in a quantum field and that for the case of the bipolaron the resulting electron?electron interaction in a phonon field depends on the electron coordinate difference alone. Predictions using a revised solution of the nonlinear differential equations for a bipolaron are given. It is shown that solving bipolaron equations numerically reduces the total bipolaron energies compared to known variational results.

Exciton effects in soliton and bipolaron lattice states of doped electron-phonon Peierls systems

Abstract: Exciton effects on soliton and bipolaron lattice states are investigated using an electron-lattice Peierls model with long-range Coulomb interactions. The systems discussed are degenerate and non-degenerate conducting polymers. The Hartree-Fock (HF) approximation and the single-excitation configuration interaction (single-CI) method are used to obtain optical absorption spectra. We discuss the following properties. (1) The attraction between the excited electron and the remaining hole makes the excitation energy smaller when the correlations are taken into account by the single CI. The oscillator strengths of the lower excited states become relatively larger than in the HF calculations. (2) We look at variations of relative oscillator strengths of two or three kinds of exciton described by the single CI. While the excess electron concentration is small, the ratio of the oscillator strengths of the exciton with the lowest energy, which is calculated against the total electronic excitation oscillator strengths, increases almost linearly. The oscillator strengths accumulate at this exciton as the concentration increases.

Intermolecular polaron and bipolaron tunneling in C60.

Abstract: Intermolecular tunneling of polarons and bipolarons is studied in ${\mathrm{C}}_{60}$ in the limit of weak electron-electron interactions. It is shown that the effective mass of the polaron is renormalized only weakly by intramolecular electron-phonon interactions. However, using the adiabatic approximation, it is found that the Franck-Condon effect would essentially localize the bipolaron on a single molecule in the limit of narrow conduction bandwidth. Indeed, the effective mass of the bipolaron would be increased by more than a factor of ${10}^{3}$. Combined with the observed metallic behavior of doped ${\mathrm{C}}_{60}$, this suggests that either the electronic correlation effects are important or that the conduction band is not too narrow in order to suppress the artificially large mass renormalization or to inhibit the bipolaron formation altogether.

Hall effect plateaus and giant Shubnikov-de Haas oscillations in (Bi\(\)Sb\(\))\(\)Te\(\)layered single crystals near the quantum limit

Abstract: On bulk layered single crystals (Bi0.25Sb0.75)2Te3 with a hole concentration cm-3 and a mobility cm2/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the damping of the amplitudes with increasing temperature the cyclotron mass m c = 0.12m 0 is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be .

Reply to "Mechanisms for ac conduction in rf sputtered Si O 2 films"

Abstract: It is again shown that the ac transport in $a\ensuremath{-}\mathrm{S}\mathrm{i}{\mathrm{O}}_{2}$ could be dominated by the correlated barrier hopping (CBH) of single polarons. It is concluded that there are difficulties in interpreting the experimental data using the bipolaron CBH and single-polaron tunneling model proposed by Meaudre and Meaudre.