The Iron Pnictide Superconductors (eBook)

CURRICULUM VITAE Ferdinando ManciniFerdinando Mancini is Professor Emeritus of Structure of Matter of the Department of Physics, University of Salerno (Italy), and President of the “International Institute for Advanced Scientific Studies”. During his very long career he has matured professional experience in Quantum Field Theory, Statistical Mechanics and Condensed Matter Physics focusing on Highly Correlated Systems, Superconductivity, Ferromagnetism and Heavy-Fermion Systems. After graduating in Physics at Naples University in 1966, he completed his Ph.D in Physics in 1971  at the University of Wisconsin-Milwaukee (USA). After his graduation, from 1971 to 1997, he visited numerous international institutions as a Visiting Scientist. Among these we find: the Dept. of Physics, Hyderabad University (India); the Dept. of Physics, Tohoku University (Sendai, Japan); the Dept. of Physics, Alberta University (Canada); the Dept. of Physics, Wisconsin-Milwaukee University (USA). During his career he has covered many positions: (1980 – 2011) Full professor of Structure of Matter, University of Salerno; (1/11/1976 - 31/10/1980) Associated Professor, University of Salerno; (1/11/1972 - 31/10/1976) Assistant Professor, University of Salerno; (1/11/1971- 31/10/1972) Assistant Professor of Physics II, University of Naples; (1/11/1968 - 31/10/1971) Research Assistant, University of Wisconsin–Milwaukee, USA; (1966 - 1968) Fellowship, Istituto di Fisica Teorica, University of Naples. Prof. Mancini has been Chairman of the Department of Physics from 01.01.84 to 31.10.89 and from 01.01.01 to 31.12.06, Member of the Board of Governors of the University of Salerno from 01.01.84 to 31.10.98, President of the University Scientific Commission from 19.01.88 to 12.06.92, President of the Undergraduate Board in Physics from 01.11.89 to 12.09.93. Prof. Mancini has carried out many National and International Scientific Collaborations: He was delegate for Italy in the "Management Committee" of the COST Action P 16 "Emergent Behaviour 3="" scientific="" events="" among="" which:="" training="" courses,="" conferences,="" symposiums="" meetings. CURRICULUM VITAECitro RobertaDr. Roberta Citro is an Associate Professor at the Department of Physics of the University of Salerno (Italy). In recent years she has matured professional experience in many-body techniques of low-dimensional systems and in quantum transport in nanostructures. She has recently established a new research team/activity on quantum transport in low dimensional systems. She completed her Ph.D in Physics at the University of Salerno (Italy) in 1998 defending a thesis on high-temperature superconductors. After her graduation, she was, first, a Post Doc Fulbright fellow at the Physics Department of Rutgers University (New Jersey, USA) where she collaborated with the Condensed Matter theory group, completing original works on the puzzling phase diagram of coupled spin chains by means of bosonizations and renormalization group methods. In 2007 she was a Marie Curie fellow under the EU’s Sixth Framework Programme-Mobility Action at the Laboratoire de Physique et Modélisation des Milieux Condensés (LPMMC, CNRS) in Grenoble (FR) where she collaborated with Dr. Anna Minguzzi and Prof. Frank Hekking. Here she acquired knowledge in the field of atomic and molecular systems, working on the problem of non-equilibrium dynamics of a Bose gas subjected to a time-dependent perturbation. She has an active synergetic activity (Member of the organizing committees of five international conferences on quantum gases and a national meeting in superconductivity, member of the Doctorate collegium, referee of the APS and IOP Journals, of Nature and of national/EU research projects). Dr. Roberta Citro is author of 125 articles published in international peer-reviewed journals (1 Rev. Mod. Phys., 4 Phys. Rev. Lett., 6 Rapid Communications, 3 Eur. Phys. Lett. and APL, 43 among Physical Review B and A). She has h-index 18 (from ISI web) and the total number of citations is more than one thousand. She has one book as co-editor published by the American Institute of Physics “Highlights in Condensed Matter Physics” (2003); she is co-editor of a topical issue of the European Physical Journal B entitle “Novel Quantum Phases and Mesoscopic Physics in Quantum Gases”, vol. 68 (2009) and of the volume European Physical Journal ST, vol 217 pags. 1-220 (2013). She has delivered thirty-two invited oral contributions at international conferences. Prizes/awards: Italian Physical Society Award (1998) and Fulbright Award (1999). 

Preface 6
Contents 7
Contributors 10
1 Iron Based Supercondutors: Introduction to the Volume 11
References 15
2 Itinerant Magnetic Order and Multiorbital Effects in Iron-Based Superconductors 17
2.1 Introduction 17
2.2 A Primer: Spin Density Wave and Spin Waves in the Single-Band Hubbard Model 19
2.3 Selection of Magnetic Order in the Parent Phase of Iron Based Superconductors 22
2.3.1 Magnetic Frustration 22
2.3.2 Lifting the Magnetic Ground State Degeneracy at TN 25
2.4 Orbital Structure of Spin Density Wave State 28
2.4.1 Transformation from Orbital to Band Basis 30
2.4.2 Spin Density Wave Mean Field Equations 32
2.4.3 Numerical Results 35
2.5 Orbital Effects for the Superconducting State 36
2.5.1 Leading Angular Harmonics Approximation 40
2.5.2 Superconductivity with the Bare Interactions 43
2.6 Spin Waves in Itinerant Multiorbital Systems 47
2.6.1 Multiorbital Models - Spin Wave Theory 48
2.6.2 Itinerant Frustration and Accidental Zero Modes 51
2.6.3 Two Orbital Model: Orbital Versus Excitonic Scenario 53
2.6.4 Comparison to Experiments 57
2.7 Discussion 59
References 59
3 Nematic Order and Fluctuations in Iron-Based Superconductors 62
3.1 Introduction 62
3.1.1 In the Search for Nematic Phases 63
3.1.2 The Ising Nematic State in Iron-Based Superconductors: Brief Introduction, Current State of the Art and Open Questions 63
3.2 Summary of Collective Field Theories of Magnetism 65
3.2.1 Hertz-Millis Theory of Magnetism 65
3.2.2 Introducing the Large-N Approach 72
3.3 Emergent Nematic Order in Iron Based Systems 75
3.3.1 Heuristic Picture of the Spin-Driven Nematic Scenario 75
3.3.2 Order-Parameter Theory of Stripe-density-wave Phase 77
3.3.3 Ising-Nematic Order 82
3.3.4 Sketch of the Phase Diagram 83
3.4 Elastic Coupling and Spin-Driven Nematicity in Iron-Based Superconductors 84
3.4.1 Elastic Theory of a Tetragonal System 85
3.4.2 Model 86
3.4.3 4 Theory of Nematic Degrees of Freedom 87
3.4.4 Estimate of the Mean-Field Regime of Nematic Degrees of Freedom 94
3.5 Physical Observables 95
3.5.1 Softening of the Elastic Modulus in the Vicinity of the Nematic Transition 95
3.5.2 Resistivity Anisotropy 98
3.5.3 Raman Spectroscopy in the Tetragonal Phase 101
3.5.4 Raman Resonance Mode in the Superconducting State 114
3.5.5 Magnetic Spectrum 118
3.6 Nematic Fluctuations and Pairing 119
References 120
4 Modeling Many-Body Physics with Slave-Spin Mean-Field: Mott and Hund's Physics in Fe-Superconductors 124
4.1 The Theoretical Description of Iron-Based Superconductors 124
4.2 Strong Electronic Correlations 127
4.2.1 The Band Theory of Solids: A Brief Reminder 127
4.2.2 Electron--Electron Interactions and Correlations 131
4.2.3 The Mott Transition and Mott Insulators 132
4.2.4 Fermi-Liquids and Effective Mass 134
4.3 The Hubbard Model 137
4.3.1 Complement: Single-Band Hubbard Model at Particle-Hole Symmetry 139
4.3.2 Which Materials Are Likely to Be Strongly Correlated? 141
4.4 Slave-Particle Approaches 142
4.5 The Slave-Spin Formalism and Its Mean-Field 144
4.5.1 Mean-Field Approximation 148
4.5.2 Complement: Derivation of the Gauge c for Arbitrary Filling 151
4.5.3 Complement: Fermi-Liquid Quasiparticle Weight and Mass Enhancement 153
4.5.4 The Half-Filled Single-Band Hubbard Model 154
4.5.5 Complement: Critical U for the Mott Transition in the Single-Orbital Hubbard Model 155
4.5.6 The Hubbard Model for Finite Doping 156
4.6 Multi-orbital Correlations: Hund's Coupling 157
4.6.1 Complement: Particle-Hole Symmetry in the Multi-orbital Hubbard Model 160
4.6.2 Extension of the Slave-Spin Formalism to Multi-orbital Hubbard Models 160
4.6.3 The N-Orbital Hubbard Model 162
4.6.4 Complement: Critical U for the Mott Transition in the 2-Orbital Hubbard Model 164
4.6.5 Effect of Hund's Coupling on the Mott Transition 166
4.6.6 The Physics of the Mott Gap 168
4.6.7 Hund's Effect on Orbital Fluctuations and the Narrowing of the Hubbard Bands 170
4.6.8 Complement: Comparison with DMFT 174
4.6.9 Complement: Critical U for the Mott Transition in the 2-Orbital Hubbard Model for Large Hund's Coupling J, and Orbital Decoupling 175
4.6.10 Hund's-Induced Orbital Decoupling 178
4.7 Slave-Spin Modeling of Fe-Based Superconductors 180
4.8 Concluding Remarks 187
References 192
Index 195