Nanoscience and Engineering in Superconductivity (eBook)

Preface 6
Contents 10
Contributors 16
1 Guided Vortex Motion and Vortex Ratchets in Nanostructured Superconductors 20
1.1 Introduction 20
1.2 Equation of Motion 21
1.3 Guided Vortex Motion 24
1.3.1 Transverse Electric Field and Guided Vortex Motion 24
1.3.1.1 Pinning-Free Superconductors 24
1.3.1.2 Superconductors with One-Dimensional Pinning 24
1.3.2 Experimental Results and Theoretical Investigations 25
1.3.2.1 Superconductors with One-Dimensional Pinning 25
1.3.2.2 Superconductors with Two-Dimensional Pinning 28
1.4 Ratchets 30
1.4.1 Basic Ingredients 32
1.4.2 Experimental Considerations 32
1.4.3 Experimental Results and Theoretical Investigations 34
1.4.3.1 Temperature Dependence 35
1.4.3.2 Sign Reversals at High Particle Densities 36
1.4.3.3 Single Vortex Rectifiers 37
1.4.3.4 Magnetic Vortex Rectifiers 38
1.4.3.5 Breaking the Time Reversal Symmetry 39
1.5 Conclusion 39
References 40
2 High-Tc Films: From Natural Defects to Nanostructure Engineering of Vortex Matter 44
2.1 Introduction 44
2.2 Vortex Matter in High-Tc Superconductors 48
2.2.1 Vortex Motion in Ideal Superconductors 48
2.2.2 Flux Pinning and Summation Theories 49
2.2.3 Pinning Mechanism in HTS 54
2.3 Vortex Manipulation in HTS Films 54
2.3.1 Vortex Manipulation via Artificial Structures 55
2.3.2 Theoretical Considerations of Vortex Manipulation via Antidots 58
2.3.3 Experimental Demonstration 64
2.3.3.1 Vortex–Antidot Interaction and Multi-Quanta Formation 65
2.3.3.2 Guided Vortex Motion via Antidots 69
2.4 Vortex Matter in Superconducting Devices 75
2.4.1 Low-Frequency Noise in SQUIDs 77
2.4.1.1 Manipulation of the Low-Frequency Noise via Antidot Arrays 81
2.4.1.2 Noise Reduction via Strategically Positioned Antidots 83
2.4.2 Vortex Matter in Microwave Devices 85
2.4.2.1 Impact of Vortices on the Microwave Properties 87
2.4.2.2 Concepts for HTS Fluxonic Devices 91
2.5 Conclusions 93
References 94
3 Ion Irradiation of High-Temperature Superconductors and Its Application for Nanopatterning 99
3.1 Introduction 99
3.2 Defect Creation by Ion Irradiation 101
3.2.1 Methods 101
3.2.2 Ion Species 102
3.2.3 Ion Energy Dependence 103
3.2.4 Angle Dependence 106
3.2.5 Experimental Results 107
3.3 Electrical Properties after Ion Irradiation 108
3.3.1 Brief Review 108
3.3.2 Experimental Techniques 109
3.3.3 Resistivity 109
3.3.4 Hall Effect 111
3.3.5 Long-term Stability 114
3.4 Nano-patterning by Masked Ion Beam Irradiation 116
3.4.1 Previous Attempts to Nanopatterning of HTS 116
3.4.2 Computer Simulation Results 117
3.4.3 Experimental Patterning Tests 118
3.5 Conclusions and Outlook 119
References 120
4 Frontiers Problems of the Josephson Effect: From Macroscopic Quantum Phenomena Decayto High-TC Superconductivity 123
4.1 Introduction 123
4.2 Grain Boundary Junctions: The Tool 124
4.3 Retracing d-wave Order Parameter Symmetryin Josephson Structures 128
4.4 Macroscopic Quantum Phenomena in Josephson Systems: Fundamentals and Low Critical Temperature Superconductor Junctions 132
4.4.1 Resistively and Capacitively Shunted Junction Model and the ``Washboard'' Potential 132
4.4.2 Macroscopic Quantum Tunnelling (MQT) and Energy Level Quantization (ELQ) 134
4.4.3 Developments of Quantum Measurements for Macroscopic Quantum Coherence Experiments 136
4.5 Macroscopic Quantum Effects in High-TC Josephson Junctions and in Unconventional Conditions 138
4.5.1 Macroscopic Quantum Phenomena in High-TC Josephson Junctions 138
4.5.2 Switching Current Statistics in Moderately Damped Josephson Junctions 143
4.5.3 MQT Current Bias Modulation 144
4.6 Mesoscsopic Effects and Coherence in HTSNanostructures 145
4.7 Conclusions 147
References 148
5 Intrinsic Josephson Tunneling in High-TemperatureSuperconductors 154
5.1 Introduction 154
5.2 Sample Fabrication 157
5.2.1 Simple Mesa 157
5.2.2 Flip-Chip Zigzag Bridges 158
5.2.3 Other Methods 159
5.3 Electrical Characterization 160
5.3.1 I-V Curves of Intrinsic Josephson Junctions in Bi2212 160
5.3.2 Critical Current Density of Individual CuO Plane 161
5.3.3 Superconducting Critical Current of Individual CuO Planes in Bi2212 161
5.3.4 Tunneling Spectroscopy 166
5.3.5 THz Radiation 169
5.3.6 Joule Heating in Mesas 172
5.3.7 The C-Axis Positive and Negative Magneto-Resistance in a Perpendicular Magnetic Field 174
5.4 Summary 176
References 176
6 Stacked Josephson Junctions 179
6.1 Introduction 179
6.2 Model 179
6.2.1 Numerical Method 184
6.2.2 Analytic Solutions 185
6.3 Bunching of Fluxons 186
6.3.1 Bunching due to Coupling Between Equations 186
6.3.2 Bunching due to Boundary Conditions 191
6.3.3 External Microwave Signal 194
6.3.4 External Cavity 195
6.4 Experimental Work 200
6.5 Summary 201
References 201
7 Point-Contact Spectroscopy of Multigap Superconductors 203
7.1 Point-Contact Andreev Reflexion Spectroscopy 204
7.2 Two Gaps in MgB2 and Doped MgB2 Systems 205
7.2.1 MgB2 205
7.2.2 Aluminum and Carbon-Doped MgB2 211
7.3 Multiband Superconductivity in the 122-type Iron Pnictides 219
7.4 Conclusions 224
References 224
8 Nanoscale Structures and Pseudogap in Under-doped High-Tc Superconductors 227
8.1 Introduction 227
8.2 Microscopic Origin of Two Types of Charge Carriers 230
8.3 Pseudogap and Two Types of Charge Carriers 236
8.4 Nanostructures in STM Measurements 241
8.5 Conclusions 244
References 244
9 Scanning Tunneling Spectroscopy of High Tc Cuprates 246
9.1 Introduction 246
9.2 Basic Principles of the STM/STS Technique 247
9.2.1 Operating Principles 247
9.2.2 Topography 248
9.2.3 Local Tunneling Spectroscopy 249
9.2.4 STS of Superconductors 250
9.3 Spectral Characteristics of HTS Cuprates 251
9.3.1 General Spectral Features of HTS Cuprates 251
9.3.2 Superconducting Gap and Pseudogap 253
9.4 Revealing Vortices and the Structureof their Cores by STS 255
9.4.1 Vortex Matter in Conventional Superconductors 256
9.4.2 Vortex Matter in HTS 257
9.4.2.1 Y-123 257
9.4.2.2 Bi-2212 258
9.4.3 Electronic Structure of the Cores 258
9.4.3.1 BCS Superconductors 258
9.4.3.2 High-Temperature Superconductors 259
9.5 Local Electronic Modulations seen by STM 261
9.5.1 Local Modulations of the Superconducting Gap 262
9.5.2 Local Modulations of the DOS 264
9.5.2.1 Modulations in the Superconducting and Pseudogapped Regimes 264
9.5.2.2 Modulations in the Vortex Cores 265
9.5.3 Summary 266
References 267
10 Scanning Tunnelling Spectroscopy of Vortices with Normal and Superconducting tips 271
10.1 Introduction 271
10.2 Experimental: Low Temperature STM with Superconducting tips 273
10.2.1 Low Temperature STM 273
10.2.2 Tips Preparation and Characterization 274
10.2.3 Spectroscopic Advantages of Superconducting tips 276
10.3 Vortices Studied by STS 279
10.3.1 The Vortex Lattice: General Propertiesand Visualization 279
10.3.2 NbSe2 Studied with Normal and Superconducting tips 280
10.3.3 NbSe2 vs. NbS2 283
10.3.4 The Vortex Lattice in thin Films: A 2D Vortex Lattice 285
10.4 Other Scenarios for the Interplay of Magnetism and Superconductivity 287
10.5 Summary and Prospects 291
References 292
11 Surface Superconductivity Controlled by Electric Field 295
11.1 Introduction 295
11.2 Limit of Large Thomas–Fermi Screening Length 296
11.3 de Gennes Approach to the Boundary Condition 298
11.4 Link to the Limit of Large Screening Length 301
11.5 Electric Field Effect on Surface Superconductivity 303
11.5.1 Nucleation of Surface Superconductivity 303
11.5.2 Solution in Dimensionless Notation 304
11.5.3 Surface Energy 307
11.6 Magneto-capacitance 308
11.6.1 Discontinuity in Magneto-capacitance 309
11.6.2 Estimates of Magnitude 309
11.7 Summary 310
References 311
12 Polarity-Dependent Vortex Pinning and Spontaneous Vortex–Antivortex Structures in Superconductor/Ferromagnet Hybrids 312
12.1 Introduction 312
12.2 Theoretical Description of F–S Hybrids 313
12.2.1 Ginzburg–Landau Theory 313
12.2.2 London Theory 317
12.3 Experimental Results 320
12.3.1 Scanning Hall Probe Imaging 320
12.3.2 Low Moment Dot Arrays with Perpendicular Magnetisation 321
12.3.3 High Moment Dot Arrays with Perpendicular Magnetisation 324
12.3.4 High Moment Arrays with In-Plane Magnetisation 328
12.3.4.1 Arrays of Rectangular Nanobars 328
12.3.4.2 Arrays of Nanoscale Ferromagnetic Rings 331
12.4 Conclusions 333
References 334
13 Superconductor/Ferromagnet Hybrids: Bilayersand Spin Switching 336
13.1 Introduction 336
13.2 Some History of the Field 337
13.3 Sample Preparation and Ferromagnet Characteristics 340
13.4 Interface Transparency 342
13.5 Domain Walls in S/F Bilayers 346
13.5.1 Domain Walls in Nb/Cu43Ni57 347
13.5.2 Domain Walls in Nb/Py 349
13.6 On the Superconducting Spin Switch 352
13.6.1 Spin Switch Effects with CuNi 353
13.6.2 Spin Switch Effects with Py 354
13.7 Concluding Remarks 356
References 358
14 Interplay Between Ferromagnetism and Superconductivity 361
14.1 Introduction 361
14.2 Artifical Synthesis: FS Hybrid Structures 363
14.2.1 Basic Physics 363
14.2.1.1 Proximity Effect and Andreev Reflection 364
14.2.1.2 Non-monotonous Decay of Superconductivity 364
14.2.1.3 Spin-dependent Interfacial Phase-shifts 365
14.2.1.4 Odd-frequency Pairing 366
14.2.2 Quasiclassical Theory 367
14.2.2.1 Green's Functions and Equations of Motion 367
14.2.2.2 Boundary Conditions 370
14.2.3 FS Bilayers 373
14.2.4 SFS Josephson Junctions 377
14.2.4.1 0- Oscillations of Critical Current 377
14.2.4.2 Inhomogeneous Magnetization Textures 379
14.2.4.3 Spin-Josephson Current 381
14.2.5 FSF Spin-valves 381
14.2.5.1 Controlling Tc by a Spin-switch 381
14.2.5.2 Crossed Andreev Reflection and Entanglement 383
14.2.6 Future Prospects 385
14.3 Intrinsic Coexistence: Ferromagnetic Superconductors 386
14.3.1 Experimental Results 386
14.3.2 Phenomenological Framework 388
14.3.3 Probing the Pairing Symmetry 395
14.3.4 Future Prospects 396
References 397
Index 401