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.

The poly‐3‐hexylthiophene/NOPF6 system: A photoelectron spectroscopy study of electronic structural changes induced by the charge transfer in the solid state

Abstract: The electronic structure of poly‐3‐hexylthiophene (P3HT) is studied in the solid state with photoelectron spectroscopy, as the polymer is gradually doped from NOPF6. Solubility and processability of P3HT allow for the preparation of very clean and very thin films, which are then doped without air‐exposure. The evolution of the core level binding energies is related to the modification of the electron density on the conjugated backbone, due to the creation of polaron and bipolaron defects. Upon doping, valence spectra show a shift in the Fermi level of the system, and at saturation doping a finite density of states at the Fermi level is observed unambiguously for the first time in electrically conducting polymers with photoelectron spectroscopy. The experimental data on core and valence levels can be interpreted in terms of the formation of a polaron lattice at high doping.

d-wave Bose–Einstein condensate and tunnelling in superconducting cuprates

Abstract: Starting from the Hamiltonian, which describes holes in a doped Mott insulator with the strong electron–phonon and Coulomb interactions we show that bipolaron formation leads to a d-wave charged Bose–Einstein condensate in cuprates. It is the bipolaron energy dispersion rather than a particular pairing interaction which is responsible for the d-wave symmetry. Single-particle spectral density is derived taking into account realistic band structure and disorder in cuprates. The tunnelling and photoemission (PES) spectra are described, including the temperature independent gap observed both in the superconducting and normal states, the emission/injection asymmetry, the finite zero-bias conductance, the spectral shape in the gap region and its temperature and doping dependence, the dip–hump incoherent asymmetric features at high voltage (tunnelling) and large binding energy (PES). The interaction responsible for the high value of Tc is elucidated which is the Frohlich electron–phonon interaction.

High-Temperature Superconductivity: Experiment and Theory

Abstract: 1. Introduction.- 1.1 The Discovery of High-Temperature Superconductivity.- 1.2 A New Class of Oxide Superconductors.- 1.3 General Properties of Oxide Superconductors.- 2. Crystal Structure.- 2.1 The Structure of Ba1-xKxBiO3.- 2.2 Lai1-xMxCuO4 Compounds.- 2.2.1 The Structure of La2-xMxCuO4-y.- 2.2.2 A Phenomenological Theory of Structural Phase Transitions in La2CuO4- Based Compounds.- 2.3 Nd2-xCexCuO4 Compounds.- 2.4 Y-Ba-Cu-O-Based Compounds.- 2.4.1 The Structure of YBa2Cu3O7-y.- 2.4.2 Modifications of the YBCO Structure.- 2.5 Bi-Ca-Sr-Cu-O and Tl-Ca-Ba-Cu-O Compounds.- 3. Antiferromagnetism in High-Temperature Superconductors.- 3.1 Antiferromagnetism in La2CuO4 Compounds.- 3.1.1 Magnetic Structure.- 3.1.2 A Phenomenological Theory of Magnetic Phase Transitions in La2CuO4.- 3.1.3 Spin Dynamics in La2?xMxCuO4.- 3.2 Antiferromagnetism in YBa2Cu3O6+x Compounds.- 3.2.1 The Magnetic Phase Diagram.- 3.2.2 Spin Dynamics in YBa2Cu3O6+x.- 3.2.3 Antiferromagnetism of Rare-Earth Ions in REBa2Cu3O6+x.- 3.3 Spin Dynamics Studied by the NMR Method.- 3.3.1 The Knight Shift.- 3.3.2 Spin-Lattice Relaxation.- 4. Thermodynamic Properties of High-Temperature Superconductors.- 4.1 The Anisotropic Ginsburg-Landau Model.- 4.2 Specific Heat.- 4.3 Magnetic Properties.- 5. Electronic Properties of High-Tc Superconductors.- 5.1 Crystal Chemistry of Oxide Superconductors.- 5.2 The Effect of Impurity Substitution.- 5.3 Theoretical Electronic Band-Structure Studies.- 5.3.1 Electronic Band-Structure Calculations.- 5.3.2 Effective Hamiltonians in Models of La2CuO4.- 5.4 Experimental Studies of the Electronic Structure.- 5.4.1 High-Energy Scale Spectroscopy.- 5.4.2 Studies of the Fermi Surface.- 5.4.3 Optical Electron Spectroscopy.- 5.5 Transport Properties.- 5.5.1 Resistivity.- 5.5.2 Hall Effect.- 5.5.3 Thermopower and Heat Conductivity.- 5.6 Superconducting Gap.- 5.6.1 Tunneling Experiments.- 5.6.2 Other Experiments.- 6. Lattice Dynamics and Electron-Phonon Interaction.- 6.1 Phonon Spectra - Neutron Scattering.- 6.2 Optical Investigations.- 6.3 Theoretical Models.- 7. Theoretical Models of High-Temperature Superconductivity.- 7.1 Quasi-Particles in Models with Strong Correlation.- 7.1.1 Model Hamiltonians.- 7.1.2 The One-Hole Quasi-Particle Spectrum.- 7.1.3 Spin Fluctuation Spectrum.- 7.2 Superconductivity in Systems with Strong Correlations.- 7.2.1 Unconventional Ground States.- 7.2.2 Superconductivity in the t-J Model.- 7.2.3 Superconductivity in the p-d Model.- 7.3 Antiferromagnetism and Superconductivity.- 7.4 Electron-Phonon Mechanism.- 7.4.1 Isotope Effect.- 7.4.2 Strong Electron-Phonon Coupling.- 7.4.3 Anharmonic Model of a Superconductor.- 7.4.4 Polarons and Bipolaron Superconductivity.- 7.4.5 Weak Coupling in the Quasi-Two-Dimensional Lattice.- 7.4.6 Spin-Fluctuation and Electron-Phonon Interactions.- 7.5 Exciton Models.- 7.5.1 Plasmon Model.- 7.5.2 Jahn-Teller Excitations and the d-d Model.- 7.5.3 Coulomb Interaction in the Multiband Models.- 8. Conclusion.- References.

Experimental evidence for bipolaron condensation as a mechanism for the metal-insulator transition in rare-earth nickelates.

Abstract: Many-body effects produce deviations from the predictions of conventional band theory in quantum materials, leading to strongly correlated phases with insulating or bad metallic behavior. One example is the rare-earth nickelates RNiO3, which undergo metal-to-insulator transitions (MITs) whose origin is debated. Here, we combine total neutron scattering and broadband dielectric spectroscopy experiments to study and compare carrier dynamics and local crystal structure in LaNiO3 and NdNiO3. We find that the local crystal structure of both materials is distorted in the metallic phase, with slow, thermally activated carrier dynamics at high temperature. We further observe a sharp change in conductivity across the MIT in NdNiO3, accompanied by slight differences in the carrier hopping time. These results suggest that changes in carrier concentration drive the MIT through a polaronic mechanism, where the (bi)polaron liquid freezes into the insulating phase across the MIT temperature.

Polyaniline emeraldine salt in the amorphous solid state: polaron versus bipolaron.

Abstract: The polaronic and bipolaronic forms of polyaniline emeraldine salt (PAni-ES) in the amorphous solid state have been simulated using classical molecular dynamics (MD) and hybrid quantum mechanical/molecular mechanical-molecular dynamics (QM/MM-MD) approaches. It should be remarked that the electronic state of PAni-ES has been theoretically investigated in the gas phase, solution phase, and crystalline state, but this is the first study in the amorphous solid state, which is the most typical for this conducting polymer. MD simulations were carried out using force-field parametrizations explicitly developed for polaronic and bipolaronic models. QM/MM-MD calculations were performed using a quantum mechanical zone defined by four repeat units. In addition of the structural and electronic characteristics of the two forms of PAni-ES, MD and QM/MM-MD simulations indicate that the bipolaronic is the most stable state of amorphous PAni-ES. Complementary studies have been carried out using different experimental techniques. Although the morphology and topography of doped and undoped PAni are very similar, comparison of their UV-vis spectra supports the preference toward the bipolaronic form of PAni-ES.