High-tc Superconductors Based on Feas Compounds

by Izyumov, Yuri; Kurmaev, Ernst

• ISBN13: 9783642145292
• ISBN10: 3642145299
• Format: Hardcover
• Copyright: 2010-11-29
• Publisher: Springer Verlag

Summary

Physical properties and models of electronic structure are analyzed for a new class of high-TC superconductors which belong to iron-based layered compounds. Despite their variable chemical composition and differences in the crystal structure, these compounds possess similar physical characteristics, due to electron carriers in the FeAs layers and the interaction of these carriers with fluctuations of the magnetic order. A tremendous interest towards these materials is explained by the prospects of their practical use. In this monograph, a full picture of the formation of physical properties of these materials, in the context of existing theory models and electron structure studies, is given. The book is aimed at a broad circle of readers: physicists who study electronic properties of the FeAs compounds, chemists who synthesize them and specialists in the field of electronic structure calculations in solids. It is helpful not only to researchers active in the fields of superconductivity and magnetism, but also for graduate and postgraduate students and all those who would like to get acquaintained with this vivid area of the materials science.

Table of Contents

Introduction	p. 1
Compounds of the ReOFeAs Type	p. 5
Crystallochemistry and Basic Physical Properties of Doped Compounds	p. 5
Crystal Structure	p. 5
Electron Doping	p. 5
Hole Doping	p. 8
Substitutions on the Fe Sublattice	p. 9
Superconducting Transition Temperature	p. 11
Critical Fields	p. 13
Effect of Pressure on the Tc	p. 14
Magnetic Properties	p. 18
Magnetic Structure	p. 18
Theoretical Explanation of Long-Range Magnetic Ordering in ReOFeAs	p. 20
Phase Diagrams	p. 24
Magnetic Fluctuations	p. 27
Electronic Structure	p. 28
Stoichiometric Compounds	p. 28
The Role of Magnetic Ordering and Doping	p. 34
Experimental Studies of the Fermi Surface	p. 38
Symmetry of the Superconducting Order Parameter	p. 41
Experimental Methods of Determining the Order Parameter	p. 41
Nuclear Magnetic Resonance	p. 42
Point-Contact Andreev Reflection	p. 46
Tunnel and Photoemission Spectroscopies (STS, PES, ARPES)	p. 53
Compounds of the AFe2As2 (A = Ba,Sr,Ca) Type	p. 57
Crystal and Electronic Structure	p. 57
Crystal Structure	p. 57
LDA Calculations of the Electronic Structure	p. 58
Experimental Studies of the Fermi Surface	p. 63
(Sr3Sc2O5)Fe2As2 and Other Similar Compounds	p. 69
Superconductivity	p. 72
Doping	p. 72
Coexistence of Superconductivity and Magnetism	p. 77
Effect of Pressure	p. 79
Symmetry of the Superconducting Order Parameter	p. 88
Measurements on the Josephson Contacts	p. 94
Critical Fields	p. 96
Magnetism	p. 98
Stoichiometric Compounds	p. 98
Doped Compounds	p. 102
Magnetic Excitations	p. 104
Other FeAs-Based Compounds	p. 109
Compounds of the FeSe, FeTe Type	p. 109
Superconducting Properties	p. 109
Unusual Magnetic Properties	p. 112
Electronic Structure of Stoichiometric Compounds	p. 115
Electronic Structure of Doped Compounds	p. 118
Magnetic Structure of FeTe	p. 120
Compounds of the LiFeAs Type	p. 122
Superconductivity	p. 122
Electronic Structure	p. 123
Compounds of the AFFeAs (A = Sr, Ca) Type	p. 126
Primary Experimental Observations	p. 126
Electronic Structure	p. 128
Theory Models	p. 131
General Properties of Compounds from Different Classes of FeAs-Systems and Corresponding Theory Objectives	p. 131
Crystal and Magnetic Structures	p. 131
Peculiarities of the Electronic Structure	p. 134
Asymmetry of the Electron/Hole Doping	p. 136
Problems of Symmetry of the Superconducting Order Parameter	p. 138
Isotopic Effect	p. 140
Role of Electron Correlations	p. 141
Dynamical Mean Field Theory (DMFT)	p. 141
LDA+DMFT Calculation for ReOFeAs Compounds	p. 145
LDA+DMFT Calculation on an Extended Basis	p. 148
Comparison with Experiment	p. 152
A Minimal Two-Orbital Model	p. 158
Formulation of the Model	p. 158
Band Structure of the Spectrum	p. 162
Mean Field Approximation	p. 164
Numerical Calculation for Small Clusters	p. 167
Multi-Orbital Model	p. 170
Formulation of the Model	p. 170
Equations for a Superconductor in the Fluctuation Exchange (FLEX) Approximation	p. 171
Properties of Superconductors with the s± Symmetry of the Order Parameter	p. 174
Three-Orbital Model	p. 178
Detailed Analysis of the 5-Orbital Model	p. 182
The Hamiltonian of the Model	p. 182
Spin and Charge Susceptibility	p. 184
Pairing of Electrons via Spin Fluctuations	p. 187
Possible Symmetries of the Superconducting Order Parameter	p. 190
Limit of Weak Coulomb Interaction	p. 194
Renormalization Group Analysis	p. 194
Equations for Superconducting and Magnetic Order Parameters	p. 202
Phase Diagram of the Model	p. 205
Peculiarities of the s±-Superconducting State	p. 207
The Limit of Strong Coulomb Interaction	p. 210
The t - J1 - J2-Model	p. 210
Superconductivity with Different Order Parameters	p. 212
Density of States and Differential Tunnel Conductivity	p. 215
The Hubbard Model with the Hund's Exchange	p. 217
Magnetic Long-Range Order and Its Fluctuations	p. 221
Two Approaches to the Problem	p. 221
The Itinerant Model	p. 224
The Localized Model: Spin Waves	p. 228
The Resonance Mode	p. 233
Unified Models	p. 240
FeAs-Compounds as Systems with Moderate Electron Correlations	p. 245
Orbital Ordering	p. 247
The Spin-Orbital Model	p. 247
Phase Diagrams with Spin and Orbital Orderings	p. 250
Spectrum of Magnetic Excitations	p. 251
Conclusion	p. 255
References	p. 259
Index	p. 277
Table of Contents provided by Ingram. All Rights Reserved.