Discovering Superconductivity: An Investigative Approach

List of Figures ix

List of Tables xiii

Preface xv

Acknowledgements xvii

To the Teacher xix

To the Student xxi

SECTION I Introduction 1

1 Resistivity and Conduction in Metals 3

1.1 Introduction 3

1.2 Resistivity 3

1.3 Conduction in Metals 5

1.4 Revisiting Ohm’s Law 7

References 11

2 A Brief History of Superconductivity 13

2.1 Introduction 13

2.2 The Beginning: Kwik Nagenoeg Nul 13

2.3 1933 – Perfect Diamagnetism? 16

2.4 The London Brothers 19

2.5 1957 – The BCS Theory 19

2.6 1962 – The Josephson Effect 21

2.7 1986 – Bednorz and Mu¨ ller and Oxide

Superconductors 22

2.8 2003 – Abrikosov, Ginzburg and Leggett – and

the Future 22

2.9 Getting Cold Enough 24

References 26

SECTION II Superconductivity 29

3 An Explanation of Superconductivity? 31

3.1 Transition Temperature 32

3.2 Two-Fluid Model 34

3.3 Critical Field, Critical Current 36

3.4 Schawlow and Devlin 38

3.5 The London Equation 39

3.6 BCS Theory 41

3.6.1 The Isotope Effect 44

3.6.2 The Energy Gap 44

3.7 An Alternative Approach to the Energy Gap 45

3.7.1 Electron–Electron Attraction 47

References 49

4 The Meissner–Ochsenfeld Effect 51

References 59

5 Diamagnetic Effects 61

5.1 Diamagnetism, Paramagnetism and Ferromagnetism 61

References 67

6 Persistence of Current 69

6.1 Quinn and Ittner 71

References 77

7 Type I and Type II Superconductors 79

7.1 Critical Magnetic Field 79

References 88

8 Flux Pinning 89

8.1 Vortex and Flux Lines 90

8.2 The Original Abrikosov 91

References 95

SECTION III Superconducting materials 97

9 Low-Temperature Superconductors 99

10 Organic Superconductors 101

References 105

11 High-Temperature Superconductors 107

11.1Magnesium Diboride 111

11.2 Transition Temperature of High-

Superconductors 112

References 114

SECTION IV Applications 115

12 Superconducting Wire 117

13 Medical Imaging 121

13.1Magnetic Resonance Imaging (MRI) 121

13.2Magnetoencephalography 122

13.2.1 Neuronal Currents 127

References 128

14 CERN and the LHC 129

References 133

15 Maglev Trains 135

Appendices 139

A The BCS Theory 141

B Flux Penetration 143

C The Josephson Junction and the SQUID 147

D MRI 151

Generating the MRI Signal 151

References 155

E A Note on Superfluidity 157

Index 163

F A Note on Safety 161

Index