Theory of Unconventional Superconductors: Cooper-Pairing Mediated by Spin Excitations (Springer Tracts in Modern Physics)

This book presents a theory for unconventional superconductivity driven by spin excitations. Using the Hubbard Hamiltonian and a self-consistent treatment of the spin excitations, the interplay between magnetism and superconductivity in various unconventional superconductors is discussed. In particular, the monograph applies this theory for Cooper-pairing due to the exchange of spin fluctuations to the case of singlet pairing in hole- and electron-doped high-__T~c~__ superconductors, and to triplet pairing in Sr~2~RuO~4~. Within the framework of a generalized Eliashberg-like treatment, calculations of both many normal and superconducting properties as well as elementary excitations are performed. The results are related to the phase diagrams of the materials which reflect the interaction between magnetism and superconductivity. Title......Page 1 Preface......Page 4 Contents......Page 5 1 Introduction......Page 8 Layered Materials and Their Electronic Structure......Page 10 La2-xSrxCuO4......Page 11 YBa2Cu3O6+x......Page 12 Nd2-xCexCuO4......Page 13 General Phase Diagram of Cuprates and Main Questions......Page 14 Normal--State Properties......Page 15 Superconducting State: Symmetry of the Order Parameter......Page 19 Triplet Pairing in Strontium Ruthenate (Sr2RuO4): Main Facts and Main Questions......Page 22 Comparison of Cuprates and Sr2RuO4: Three--Band Approach......Page 26 Effective Theory for Cuprates: One--Band Approach......Page 29 Spin Fluctuation Mechanism for Superconductivity......Page 30 References......Page 35 Generalized Eliashberg Equations for Cuprates and Strontium Ruthenate......Page 40 Theory for Underdoped Cuprates......Page 53 Extensions for the Inclusion of a d-Wave Pseudogap......Page 55 Fluctuation Effects......Page 59 Elementary Excitations......Page 67 Superfluid Density and Transition Temperature for Underdoped Cuprates......Page 69 Raman Scattering Intensity Including Vertex Corrections......Page 72 Optical Conductivity......Page 78 Comparison with Similar Approaches for Cuprates......Page 80 The Spin Bag Mechanism......Page 81 The Theory of a Nearly Antiferromagnetic Fermi Liquid (NAFL)......Page 83 The Spin--Fermion Model......Page 84 BCS--Like Model Calculations......Page 87 Local vs. Nonlocal Correlations......Page 91 The Large-U Limit......Page 93 Projected Trial Wave Functions and the RVB Picture......Page 95 Current Research and Discussion......Page 97 References......Page 99 Hole--Doped Cuprates......Page 105 Electron--Doped Cuprates......Page 115 Interplay Between Spins and Charges: a Consistent Picture of Inelastic Neutron Scattering Together with Tunneling and Optical--Conductivity Data......Page 121 The Spectral Density Observed by ARPES: Explanation of the Kink Feature......Page 131 Electronic Raman Scattering in Hole--Doped Cuprates......Page 143 Raman Response and its Relation to the Anisotropy and Temperature Dependence of the Scattering Rate......Page 144 Collective Modes in Hole--Doped Cuprates......Page 150 A Reinvestigation of Inelastic Neutron Scattering......Page 151 Explanation of the ``Dip--Hump'' Feature in ARPES......Page 154 Collective Modes in Electronic Raman Scattering?......Page 155 Consequences of a dx2-y2--Wave Pseudogap in Hole--Doped Cuprates......Page 157 Elementary Excitations and the Phase Diagram......Page 158 Optical Conductivity and Electronic Raman Response......Page 164 Brief Summary of the Consequences of the Pseudogap......Page 173 References......Page 175 4 Results for Sr2RuO4......Page 183 Importance of Spin--Orbit Coupling......Page 185 The Role of Hybridization......Page 188 Comparison with Experiment......Page 191 Symmetry Analysis of the Superconducting Order Parameter......Page 193 Triplet Pairing Arising from Spin Excitations......Page 194 Summary, Comparison with Cuprates, and Outlook......Page 198 References......Page 203 5 Summary, Conclusions, and Critical remarks......Page 206 References......Page 213 A Solution Method for the Generalized Eliashberg Equations for Cuprates......Page 215 References......Page 218 B Derivation of the Self-Energy (Weak-Coupling Case)......Page 219 C dx2-y2-Wave Superconductivity Due to Phonons?......Page 228 Index......Page 230