Mechanisms of Conventional and High Tc

Superconductivity has become one of the most intensely studied physical phenomena of our times, with tremendous potential to revolutionize fields as diverse as computing and transportation. This book describes the methods, established results, and recent advances in the field. The goal is to present recently developed theoretical models in light of the long-sought aim of achieving the effect at very high temperatures. The book includes a detailed review of various mechanisms, including phononic, magnetic, and electronic models. The authors focus on the phenomenon of induced superconductivity in the high-temperature oxides, particularly the high-transition-temperature cuprates. They also discuss a variety of low-temperature superconducting systems in conventional materials and organics. The book links the crucial experiments with the most current theories, offering a unified description of the phenomenon. All researchers (and graduate-level) students involved with work in superconductivity will find this an invaluable resource, including solid-state and condensed-matter physicists and chemists, and materials scientists.

Introduction	p. 3
Major goals	p. 3
Historical perspective	p. 4
Phonon Mechanism	p. 6
Electron-phonon interaction	p. 6
The Hamiltonian	p. 6
Adiabatic approximation. "Crude" approach	p. 7
Electron-phonon coupling	p. 10
Superconductivity as a nonadiabatic phenomenon	p. 13
Eliashberg equations. Superconductors with strong coupling	p. 14
Self-energy parts	p. 14
General properties of the Eliashberg equations	p. 17
Critical temperature	p. 20
Weak coupling	p. 20
Intermediate coupling ([lambda] [less-than, similar] 1.5)	p. 22
Coulomb interaction	p. 24
Very strong coupling	p. 25
General case	p. 27
Properties of superconductors with strong coupling	p. 30
Electron-phonon interaction and renormalization of normal parameters	p. 34
Nonlinear electron-phonon interactions	p. 37
Phonon dynamics of perovskites	p. 37
Anharmonicity	p. 39
Bipolaronic superconductivity and negative Hubbard U-models	p. 41
Isotope effect	p. 42
Experimental Methods	p. 44
Tunneling spectroscopy	p. 44
Experimental methods	p. 44
Energy gap and transition temperature	p. 46
Inversion of the gap equation and [alpha superscript 2]F([Omega])	p. 48
Electron-phonon coupling parameter [lambda]	p. 50
Infrared spectroscopy	p. 52
Ultrasonic attenuation	p. 54
Nuclear magnetic resonance	p. 55
Electronic Mechanisms	p. 58
The Little model	p. 58
"Sandwich" excitonic mechanism	p. 61
Excitons and high T[subscript c]	p. 61
Three-dimensional systems	p. 62
Pairing of conduction electrons via interaction with localized states	p. 62
Two delocalized groups	p. 63
Negative U-centers	p. 64
Plasmons	p. 65
Overlapping bands. "Demons"	p. 65
Two-dimensional electron gas	p. 68
Coexistence of phonon and electronic mechanisms	p. 68
Magnetic Mechanisms	p. 71
Introduction	p. 71
Localized vs. itinerant aspects of the cuprates	p. 72
Fermi liquid-based theories	p. 75
The spin bag model of Schrieffer, Wen, and Zhang	p. 75
The t-J model	p. 78
Two-dimensional Hubbard model studies by Monte Carlo techniques	p. 83
Spiral phase of a doped quantum antiferromagnet	p. 92
Slave bosons	p. 97
Non-Fermi-liquid models	p. 100
The resonant valence bond (RVB) model and its evolution	p. 100
Anyon models and fractional statistics	p. 101
Conclusions	p. 102
Induced Superconductivity	p. 103
Two-band model	p. 103
General description	p. 103
Critical temperature	p. 104
Two-gap spectrum and properties of superconductors	p. 106
Induced two-band superconductivity	p. 107
Proximity effect	p. 108
Proximity "sandwich"	p. 108
Critical temperature. Induced energy gap	p. 109
Proximity effect vs. the two-gap model	p. 112
Layered systems. General case	p. 113
Hamiltonian. General equations	p. 113
Critical temperature	p. 116
Spectroscopy	p. 123
Magnetic impurities. Gapless induced superconductivity	p. 125
Major parameters	p. 126
Conventional superconductors	p. 126
High T[subscript c] Cuprates	p. 128
Introduction	p. 128
Normal properties	p. 129
One-particle excitations	p. 129
Collective excitations	p. 133
Superconducting properties	p. 137
Coherence length	p. 137
The ratio [varepsilon](0)/E[subscript F]	p. 138
Critical behavior	p. 138
Positron annihilation	p. 139
Electromagnetic properties	p. 140
Induced superconducting state and two-gap structure	p. 142
Two-gap structure. Coherence lengths	p. 143
Oxygen depletion and the gapless state	p. 144
Bi- and Tl-based cuprates	p. 146
Origin of high T[subscript c]	p. 146
Determination of carrier--phonon coupling parameter	p. 147
Critical temperature	p. 149
Discussion	p. 150
Key experiments	p. 151
Normal properties	p. 151
Superconducting properties	p. 153
Properties as a function of doping	p. 156
Organics vs. cuprates	p. 159
Why is T[subscript c] still so low in the organics?	p. 159
Superconducting fullerenes	p. 161
Future directions	p. 164
References	p. 166
Index	p. 179
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Mechanisms of Conventional and High Tc Superconductivity

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