edited by " Nan-Lin Wang Hideo Hosono Pengcheng Dai MATERIALS, PROPERTIES, AND MECHANISMS IRON-BASED SUPERCONDUCTORS Pan Stanford Publishing
Contents Preface xiii 1 Iron-Based Superconductors: Discovery and Progress in Materials 1 Hideo Hosono 1.1 Introduction 1 1.2 Small History on Discovery and Progress in Parent Materials 3 1.3 Crystal Structure of Parent Materials 6 1.3.1 1111-Type Materials (LnFePnO, Ln: Lanthanide) 6 1.3.2 122-Type Materials (AeFe2Pn2, Ae: Alkaline Earth or Eu) 9 1.3.3 Ill-Type Materials (AFePn, A: Alkali Metal) 10 1.3.4 11-Type Materials (Fe1+xSe] 10 1.3.5 Homologous-Type Materials: (Fe2As2)(Aen+1MmOy) 10 1.4 Parent Material and Superconductivity 11 1.4.1 Doping Effect 11 1.4.1.1 Thellll-type 12 1.4.1.2 Thel22-type 15 1.4.2 Local Structure and Tc 20 1.5 Unique Characteristics of FeSCs 23 1.5.1 Multi-Band Nature of Fe3d 23 1.5.2 Parent Material: Antiferromagnetic Metal 24 1.5.3 Impurity Robust Tc 25 1.5.4 Large Critical Field and Small Anisotropy 25 1.5.5 Advantageous Grain Boundary Nature 26
vi I Contents 1.6 Single Crystal 27 1.6.1 Growth of 1111-Type Crystals 27 1.6.2 Growth of the 122-Type Crystals 29 1.6.3 Characteristics of a Single Crystal 30 1.7 Thin Film 32 1.7.1 1111-Type Compounds 32 1.7.2 122-Type Compounds 35 1.7.3 11-Type Compounds 38 1.8 Summary and Relevant New Superconductors 40 2 Synthesis and Physical Properties ofthe New Potassium Iron Selenide Superconductor Ko.soFeueSez 53 R. Hu, E. D. Man, D. H. Ryan, K. Cho, H. Kim, H, Hodovanets, W. E. Straszheim, M. A. Tanatar, R. Prozorov, W. N. Rowan-Weetaluktuk, J. M. Cadogan, M. M. Altarawneh, C. H. Mielke, V. S. Zap/, S. L Bud'ko, and P. C. Canfield 2.1 Introduction 54 2.2 Experimental Methods 55 2.3 Crystal Growth and Stoichiometry 57 2.4 Physical Properties of Single Crystals of K0.8oFei.76Se2 59 2.4.1 Transport and Thermodynamic Properties 59 2.4.2 London Penetration Depth and Magneto-Optical Imaging 64 2.4.3 Anisotropic Hc2{T) 66 2.4.4 57Fe Mossbauer Spectroscopy 71 2.4.5 Phase Separation and Possible Superconducting Aerogel 79 2.5 Summary 80 3 Angle-Resolved Photoemission Spectroscopy of Iron Pnictides Takafumi Sato, Pierre Richard, Kosuke Nakayama, Takashi Takahashi, and Hong Ding 89 3.1 Introduction 90 3.1.1 Principle of ARPES 91 3.2 Experimental Results 93 3.2.1 Fermi Surface and Pairing Symmetry 93 3.2.1.1 Hole-doped system 93 3.2.1.2 Electron-doped system 104
Contents 3.2.2 Many-Body Interactions 108 3.2.3 Parent Compound 112 3.3 Concluding Remarks and Summary 115 4 Quantum Oscillations in Iron Pnictide Superconductors 125 Suchitra E. Sebastian 4.1 Quantum Oscillations 126 4.1.1 Angular Dependence 128 4.1.1.1 Fermi surface geometry 128 4.1.1.2 Spin splitting 128 4.2 Magnetic Field Dependence 129 4.3 Temperature Dependence 130 4.4 Iron Pnictide Superconductors 131 4.5 Quantum Oscillations in Antiferromagnetic Parent Iron Pnictides 131 4.5.1 Fermi Surface Geometry: Nonmagnetic and Antiferromagnetic Band Structure Calculations 134 4.5.2 Experimental Comparison with Band Structure 137 4.5.3 Dirac Nodes 141 4.6 Quantum Oscillations in Overdoped Paramagnetic Iron Pnictides 142 4.6.1 Quasi-Nesting of Hole and Electron Cylinders 144 4.7 Cuprates and Iron Pnictides: Electronic Structure Comparison 146 4.7.1 Enhancement in Lindhard Function in Pnictides and Cuprates 147 4.7.2 Quantum Critical Point under Superconducting Dome 149 4.8 Conclusion 152 5 Optical Investigation on Iron-Based Superconductors 161 Nan-Lin Wang and Zhi-Guo Chen 5.1 Introduction 161 5.2 Introduction About Optical Properties of Solids 164 5.2.1 Optical Constants 164 5.2.2 Interband and Intraband Excitations 166 5.2.3 Drude Model and Drude-Lorentz Model 168 5.2.4 Extended Drude Model 170
viii Contents 5.2.5 Sum Rules 172 5.2.6 Optical Response of Broken Symmetry States of Metals 174 5.3 Optical Studies on the Parent Compounds 176 5.3.1 Spin Density Wave Gap in FeAs-Based Compounds 177 5.3.2 Absence ofsdw Gap in FeTe1+x 182 5.3.3 Fully Localized Fe 3d Electrons in K0.sFei.6Se2 184 5.4 Multi-Components vs. Extended Drude Model Analysis of Optical Conductivity 186 5.5 Electron Correlations in the Fe-Pnictides/Chalcogenides 192 5.5.1 Kinetic Energy Reduction by Electron Correlations 192 5.5.2 Effect of Hund's Coupling 196 5.6 Anisotropic Charge Dynamics 201 5.6.1 c-axis Optical Properties in Parent Compounds 201 5.6.2 Anisotropic Optical Properties within afa-plane 204 5.6.3 c-axis Optical Properties of Superconducting Compounds 209 5.7 Optical Properties of Iron-Based Superconductors Below Tc 214 5.7.1 Probing the Superconducting Energy Gaps 214 5.7.2 Josephson Coupling Plasmon in KxFe2_),Se2 223 5.7.3 Superconductivity-Induced Spectral Weight Transfer 226 5.7.4 Coherent Peak Below Tc Probed by THz Spectroscopy 230 6 Antiferromagnetic Spin Fluctuations in the Fe-Based Superconductors 243 Shiliang Li and Pengcheng Dai 6.1 Introduction 244 6.2 Antiferromagnetism in Parent Compounds 246 6.2.1 Long-Range Antiferromagnetic Order 246 6.2.2 Spin Waves 249 6.2.3 Destruction of Antiferromagnetic Order 253
Contents ix 6.3 Magnetic Excitations in the Superconducting State 256 6.3.1 Magnetic Resonance 257 6.3.2 Field Effect on Magnetic Resonance 261 6.3.3 Field-Induced Magnetization 264 6.4 Magnetic Excitations in the Normal State 264 6.4.1 In-Plane Anisotropy in the "122" System 264 6.4.2 Incommensurate Magnetic Excitations in the "11" System 265 6.5 Conclusion 268 7 Review of NMR Studies on Iron-Based Superconductors 275 Kenji Ishida and Yusuke Nakai 7.1 Introduction 275 7.2 NMR Basics 276 7.2.1 NMR Hamiltonian 276 7.2.2 Knight Shift and Nuclear Spin-Lattice Relaxation Rate in Metals 278 7.2.3 Knight Shift and Nuclear Spin-Lattice Relaxation Rate in the Superconducting State 281 7.3 NMR Experimental Results on Iron-Based Superconductors 287 7.3.1 LaFeAs(Oi_xFx] and LaFeAsO^ with "1111" Structure 287 7.3.1.1 LaFeAsO: parent compound 288 7.3.1.2 Normal state of LaFeAstOi-xF*) and LaFeAsOi_{ 291 7.3.1.3 Superconducting state of LaFeAs(Oi_xFx)andLaFeAsOi_«299 7.3.2 NMR Study in "122" System 305 7.3.2.1 BaFe2As2 307 7.3.2.2 NMR in the normal state of BaFe2(Asi_xPx)2 313 7.3.2.3 NMR in the normal state of Ba(Fei_xCox)2As2 319 7.3.2.4 NMR in the normal state of CBai_xKx)Fe2Asz 323 7.3.2.5 NMR results on the superconducting state of "122" compounds 325
x Contents 7.3.3 NMR Study in "111" System, LiFeAs and NaFeAs 332 7.3.4 NMR Study in "11" System, FeSe 337 7.3.5 NMR Study in KxFe2-ySe2 340 7.4 Summary 346 8 Material Specific Model Hamiltonians and Analysis on the Pairing Mechanism 357 Kazuhiko Kuroki 8.1 Introduction 358 8.2 Model Hamiltonian Construction 359 8.2.1 The Band Structure 359 8.2.2 Electron-Electron Interactions 366 8.3 Spin Fluctuations and Antiferromagnetism 368 8.3.1 Random Phase Approximation 368 8.3.2 Electron-Hole Interaction 369 8.3.3 Antiferromagnetism in the Parent Compound 374 8.4 Superconductivity 378 8.4.1 General Theory on Fluctuation Mediated Pairing 378 8.4.2 Spin Fluctuation Mediated Pairing 382 8.4.3 Orbital Fluctuation Mediated Pairing 386 8.4.4 Theoretical Proposals for the Detection of the Pairing State Based on the Effective Multiorbital Hamiltonian 387 8.5 Material Dependence 390 8.5.1 Some Experimental Observations 390 8.5.2 Lattice Structure Dependence of the Band Structure and the Electron-Electron Interactions 392 8.5.2.1 Pnictogen height 392 8.5.2.2 Bond angle 395 8.5.2.3 Three dimensionality 397 8.5.3 Material Dependence of the Spin Fluctuations and Superconductivity 400 8.5.3.1 Lattice structure dependence 400
Spin Contents xi 8.5.3.2 Doping dependence 407 8.5.3.3 Effect ofthe three dimensionality 410 8.6 Concluding Remarks and Perspectives 413 9 The Antiferromagnetic Phase of Iron-Based Superconductors: An Itinerant Approach 431 Johannes Knolle and Hya Eremin 9.1 Introduction 431 9.2 A Primer: Single-Band Hubbard Model 434 9.3 Magnetic Order in Ferropnictides 437 9.3.1 Magnetic Frustration 437 9.3.2 Lifting the Magnetic Ground State Degeneracy at TN 441 9.3.3 Ising Nematic Order Above TN 445 9.4 Spin Waves in Itinerant Multiorbital Systems 448 9.4.1 Multiorbital Models Wave Theory 448 9.4.2 Accidental Collective Modes in Itinerant Frustrated Antiferromagnets 451 9.4.3 Two Orbital Model: Orbital versus Excitonic Scenario 458 9.4.4 Comparison to Experiments 464 9.5 Discussion and Conclusion 466 10 Magnetism in Parent Compounds of Iron-Based Superconductors 473 Jiangping Hit 10.1 Introduction 474 10.2 Experimental Results on the Parent Compounds of Iron-Based Superconductors 476 10.2.1 Results on Iron-Pnictides 476 10.2.2 Results on Iron-Chalcogenides 478 10.2.3 Electronic Structures and Resistivity Anisotropy 482 10.3 Theoretical Models 483 10.3.1 Results offirst Principle Electronic Structure Calculation 483 10.3.2 Effective Magnetic Exchange Models for Iron-Pnictides 485
xii Contents 10.3.3 Effective Magnetic Exchange Models for Iron-Chalcogenides 490 10.3.3.1 FeTe 491 10.3.3.2 Ao.8Fei.6Se2 495 10.3.4 A Unified Minimum Magnetic Exchange Model For Iron-Based Superconductors 498 10.4 Electronic Nematism and the Interplay Between Lattice, Spin and Orbital 503 10.5 Discussion 507 Index 513