The NMR Probe of High-Tc Materials and Correlated Electron Systems

329 Pages·2018·12.22 MB·English

by  Russell E. Walstedt (auth.)

Springer Tracts in Modern Physics 276
Russell E. Walstedt
The NMR Probe of
High-T Materials
c
and Correlated
Electron Systems
Second Edition
Springer Tracts in Modern Physics
Volume 276
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Russell E. Walstedt
T
The NMR Probe of High-
c
Materials and Correlated
Electron Systems
Second Edition
123
Russell E. Walstedt
Department ofPhysics
University of Michigan
AnnArbor, MI
USA
ISSN 0081-3869 ISSN 1615-0430 (electronic)
SpringerTracts inModern Physics
ISBN978-3-662-55580-4 ISBN978-3-662-55582-8 (eBook)
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To Erwin, Vince, and Hiroshi
Preface
Totheoldsayingthatifyouwanttolearnsomethingaboutasubject,teachacourse
on it, I would add the much more arduous option of writing a book about it. The
upside,ofcourse,isthatyoumaygainaperspectiveonalongtimefavoritesubject
which can be achieved in no other way. The fact is that the opportunity to write
suchabookasthisis,indeed,arareopportunity,especiallyforsomeonewhobythe
calendar is well into retirement years.
While for a physics researcher, high Tc itself was the opportunity of a lifetime,
and revisiting the old milestones within is a genuine nostalgia trip, it is also
important to reflect on the purpose of such a book as this. Now that the great
majority of experimental high-Tc studies are finished, who could be interested in
such a book? To give some kind of answer to this, let me pinpoint the 2006 M2S
Conference in Dresden.1 Not only was it at this conference that the idea for this
book was hatched, but the conference itself evinced an astonishingly high level of
interest in high-Tc issues, especially the theoretical aspects. Since it is now a
number of years since a review of high-Tc studies with NMR has appeared, there
may beaneed onthepart oftheoristsandother interestedparties for anorganized
summary of results and of the ideas which have been advanced to bind them
together.
The foregoing offers a partial answer to the “Why now?” question, but let me
note that excellent answers to that question also emerge from the subject, itself.
Although many issues were settled as of ten years ago, new ideas and even new
phenomena have appeared since that time. Let me offer two examples. The con-
firmationbyN.Curroandcoworkersofadynamicalexponentcrossoverinthehigh
temperaturephasediagramopensupanewarenaofpotentialexperimentalactivity.
Pinesandcoworkershadpredictedsuchaneffect;othertheorists,includingVarma,
hadpredictedaphaseboundaryinthatregion.Anotherinterpretivebreakthroughis
to be credited to Uldry and Meier, who in2005 created a new, general method for
1This was the 8th International Conference on Materials and Mechanisms of Superconductivity
andHighTemperatureSuperconductors,Dresden,July9–14,2006.
vii
viii Preface
analyzing relaxation (T ) data in terms of temperature-dependent spin-spin corre-
1
lation coefficientsfor close-neighborcopper sites.Discussed atsome lengthinthis
volume, this method rests on a very firm theoretical foundation. It has the great
virtue that it separates these correlation effects from the temperature dependence
ofthequasiparticledynamics,itself,whichtheoreticalmodelershavebeentryingto
getat.Ifthisextraordinarilysimplemethodhadbeen“available”fifteenyearsago,I
suggest that our understanding of these issues would be greatly advanced from
where it is.
As for regrets, they come mainly under the heading of omissions. There are
manyexcellentpiecesofworkwhicharenotincluded,simplyforwantoftimeand
space. The book was conceived of as a monograph and is in no sense an ency-
clopedia, not even within the narrow purview of high-Tc NMR. As an example, I
greatly regret omitting the large and fascinating subject of impurity doping in
cuprates, from which we have nonetheless learned a lot.
Let me conclude by mentioning just a few of the people who have contributed,
directlyandindirectly,totheinitiationandcreationofthisbook.Firstletmethank
Prof.HiroshiYasuoka,forbringingmetoTokai-murainJapanforafive-plusyear
extension of my career in solid-state NMR, and through which I also became
involvedintheEuropeanphysicsscene.LetmethankProf.Drs.FrankSteglichand
Jürgen Haase, for their support during my extensive stay in Dresden in 2006 (and
later).InvaluablesupportcamefromtheDepartmentofPhysicsattheUniversityof
Michigan in providing work space and the library facilities required for a project
such as this. I want especially to thank Prof. Chandra Varma of the University of
CaliforniaatRiverside,forshepherdingthisbookintoexistencethroughhisroleas
editor for Springer Verlag, and for his reading of much of the manuscript, giving
penetrating, enlightening, and invaluable comments on the presentation. I also
thankJinanYangforhelpwithcomputerissuesandwithpreparationofthefigures.
Ann Arbor, USA Russell E. Walstedt
June 2007
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 The Basic Phenomenology of High-Tc Materials . . . . . . . . . . . . . 2
1.2 Carrier Doping and the Master Phase Diagram. . . . . . . . . . . . . . . 3
1.3 The NMR Probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Outlines of the Remaining Chapters. . . . . . . . . . . . . . . . . . . . . . . 6
1.4.1 Summary of Chapter 2—NMR Review. . . . . . . . . . . . . . . 6
1.4.2 Summary of Chapter 3—Preliminary Cuprate NMR . . . . . 7
1.4.3 Summary of Chapter 4—The Pseudogap. . . . . . . . . . . . . . 7
1.4.4 Summary of Chapter 5—T Models . . . . . . . . . . . . . . . . . 9
1
1.4.5 Summary of Chapter 6—The Dynamical Susceptibility . . . 10
1.4.6 Summary of Chapter 7—NMR Studies of Actinide
Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.7 Summary of Chapter 8—The Kondo Effect
and Heavy–Fermion Behavior . . . . . . . . . . . . . . . . . . . . . 12
1.4.8 Summary of the Appendix:
The Properties of Spin Echoes . . . . . . . . . . . . . . . . . . . . . 13
2 Introduction to NMR Studies of Metals, Metallic Compounds,
and Superconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 The Fundamental Elements of NMR . . . . . . . . . . . . . . . . . . . . . . 15
2.1.1 Observation of NMR/NQR Signals. . . . . . . . . . . . . . . . . . 17
2.1.2 Definition and Interpretation of NMR Parameters: T
2
Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.1.3 The Basic Structure of NMR Spectra in Solids . . . . . . . . . 22
2.1.4 Definition and Interpretation of NMR Parameters:
The Shift Tensor Kab. . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.1.5 Definition and Interpretation of NMR Parameters: T . . . . . 29
1
2.2 NMR Probe of sp-Band Metals and Type I Superconductors. . . . . 36
2.2.1 NMR Shifts and Relaxation in Simple
Pauli Paramagnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
ix
x Contents
2.2.2 TheMoriyaTheoryofExchangeEnhancementinSimple
Metals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.2.3 NMR in the Superconducting State of Simple Metals . . . . 41
2.3 Static and Dynamic Magnetism in d-Band Metals . . . . . . . . . . . . 47
2.3.1 The d-Electron HF Interactions. . . . . . . . . . . . . . . . . . . . . 48
2.3.2 Orbital Shift and Susceptibility. . . . . . . . . . . . . . . . . . . . . 50
2.3.3 Spin-Lattice Relaxation Effects for d-Band Electrons . . . . . 53
2.3.4 NMR Studies of 3d Metals as Type-II Superconductors. . . 56
2.3.5 T1 Phenomenology for Type-II Superconductors . . . . . . . . 61
3 The Superconducting Cuprates: Preliminary Steps in Their
Investigation via NMR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.1 Cuprate Structures and Doping Effects: LSCO and YBCO . . . . . . 68
3.1.1 LSCO: A Superconductor with T (max)’40 K . . . . . . . . 68
c
3.1.2 The 92 K Superconductor YBa2Cu3O7(cid:2)x (YBCO). . . . . . . 70
3.1.3 Physical Models of Itinerant Quasiparticles in Cuprates . . . 71
3.2 Early NMR/NQR Studies: The Early Predominance of YBCO . . . 72
3.2.1 NMR Shift and Relaxation of the 89Y in YBCO7 . . . . . . . 73
3.2.2 Establishing the Site Assignment for the Cu(1)
and Cu(2) NQR Spectra. . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.2.3 Variation of the 89Y Shift K (x) with x
89
for YBCO6+x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.2.4 Physical Models for the Relaxation of 63Cu(2)
in YBCO7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2.5 Introduction of the Spin Hamiltonian Model
for the Cu2þ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.2.6 Experimental Breakthrough: Oriented Powder
Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.3 The Mila-Rice-Shastry Model: A Universal HF Tensor
for the Cuprates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.3.1 General Definition of the HF Tensors . . . . . . . . . . . . . . . . 81
3.3.2 Extracting the Cu(1, 2) HF Tensors for YBCO7
from Shift and Susceptibility Data Using the Spin
Hamiltonian Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.3.3 Quantum Chemistry of YBCO7 and the Hyperfine
Tensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.3.4 T Ratios and Electron Spin Correlation Effects . . . . . . . . 90
1
3.4 Incorporating 17O and 89Y Data into the Mila-Rice-Shastry
Picture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.4.1 Measurements of T for 17O in YBCO7 . . . . . . . . . . . . . . 96
1
3.4.2 The One-Band, Two-Band Debate: 89Y and 17O(2, 3)
NMR in YBCO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97