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Full Description
Phase separation has become a fascinating subject in the discussion of cuprate superconductors. All these materials have layered structures containing CU02 planes as the most important building blocks. They are coupled only weakly so that the electronic properties show a nearly two-dimensional behaviour. Due to correlations the undoped compounds are insulators of the Mott Hubbard type exhibiting long-range antiferromagnetic order. Upon doping a rich scenario of physical phenomena appears: Even at low hole concentra tions the antiferromagnetic ordering temperature is reduced drastically and spin-glass behaviour as well as a hopping type conductivity can be observed. Further doping leads to metallic-like conductivity and below Tc to super conductivity. In this doping regime antiferromagnetic fluctuations are still observed. At very high charge carrier densities superconductivity is lost and the systems show pure metallic conduction without ,magnetic correlations. One of the most interesting phenomena in high-T c research is the interplay between magnetism and conductivity or superconductivity. Especially the behaviour of charge carriers in the antiferromagnetic background raises a number of open questions. Two scenarios become possible: the carriers tend to delocalize over the whole crystal forming a homogeneous state with band-like structure or they separate into hole-rich (conducting, superconducting) and hole-poor (insulating, antiferromagnetic) phases leading to an inhomogeneous structure.
Contents
I General Properties.- Recipe for High-Tc Transition-Metal Chalcogenide Superconductors.- Phase Separation as a Possible Scenario for High Tc Superconductors: A Particular Overview.- Point Contact Spectroscopy in the High Tc Oxides.- Cuprate Superconductors: Universal Properties and Trends; Evidence for Bose-Einstein Condensation.- II Electronic Results I.- Polar on Formation and Percolative Phase Separation in HTSC.- On the Role of Electronic and Chemical Phase Separation: Susceptibility and Conductivity Experiments on La2?xCuO4+?.- The Phase Diagrams and Doped-Hole Segregation in La2CuO4+? and La2?xSrxCuO4+? (x ? 0.15, ? ? 0.12).- Neutron Spectroscopy in RBa2Cu3Ox (R=Rare Barth, 6?x?7) Compounds: Charge Transfer, Phase Separation, Spin Fluctuations.- III Electronic Results II.- Phase Separation in Cuprate Superconductors: Magnetic Resonance Studies.- Paramagnetic Resonance Studies of Phase Separation in Cuprate Superconductors.- Fermi Glass State in Partially Doped Insulating Cuprates.- Two-Magnon Raman Scattering in Doped YBa2Cu3Ox with Respect to Confined Hole Clusters.- IV NMR and Mössbauer Studies.- Electron Hole Ordering in La2CuO4+?.- Microscopic Study of Local Structure and Charge Distribution in Metallic La2CuO4+?.- Mössbauer Probe Measurements in La2?xSrxCuO4 and YBa2Cu3Ox.- V Structural Phase Separation.- Indications for a Phase Separation in YBa2Cu3O7?x.- Superconductivity Versus Oxygen Concentration in 123 Compounds: Influence of RE Ionic Radii Studied by Cu NQR.- The Role of the Additional Oxygen Atoms on the Superconducting Properties of La2CuO4-Related Compounds.- Structural Disorder and Phase Separation in TmBaCuO as Seen from Tm NMR.- VI Electron-Phonon Interaction I.- The Coupling of a Wigner Polaronic Charge Density Wave witha Fermi Liquid Arising from the Instability of a Wigner Polaron Crystal: A Possible Pairing Mechanism in High Tc Superconductors.- Pairing Interaction and Phonon Renormalization Favored by Phase Separation.- Electronic Excitations in Undoped and Lightly Oxygen Doped La2CuO4+y.- VII Electron-Phonon Interaction II.- Electronic Structure and High Tc Superconductivity in the Cuprates.- Apex Oxygen Anharmonicity and Low Energy Electronic Transitions Observed in 1-2-3 by IR-Excited Raman Spectroscopy.- Photoexcited Electons and Holes in YBa2Cu3O7??: A Study by Picosecond Raman Scattering.- Anharmonic Effects Related to the Apical Oxygen Vibration in YBa2Cu3O7 by LAPW Calculations.- VIII Further Theoretical Concepts.- Thermodynamics of the Emery Model.- The Effect of Coulomb Interactions on Phase Separation.- Options for the Effective Electron-Electron-Interaction from Unitary Transformations.
