Ansermet Emergent Superconductivity in Low Dimensions

1. Auflage 2018
ISBN: 978-981-13-2941-8
Verlag: Springer Nature Singapore
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 194 Seiten

Reihe: Springer Theses

This book explores the relationship between electronic correlations, dimensionality, inhomogeneities, and superconductivity in low-dimensional systems by studying single crystals of the quasi-one-dimensional Na2-?Mo6Se6, composed of MoSe filaments weakly coupled by Na atoms and subject to intrinsic disorder (? > 0). It shows that the Na2-?Mo6Se6 displays strong electronic correlations in its normal state, whereas a superconducting ground state emerges from Anderson localized electrons. Two novel behaviors of the superconducting state are observed: first, a disorder induced enhancement of the superconducting transition temperature; second, a reentrant phase coherence with increasing temperature, magnetic field, and current. It also analyzes the intrinsic properties of Na2-?Mo6Se6 are analyzed to offer a thorough understanding of these phenomena. The emergence of superconductivity in such low-dimensional systems provides a fruitful playground to explore electronic order and correlations.

Dr. Diane Ansermet completed her Bachelor's and Master's degrees at EPFL in Switzerland, where she studied Materials Sciences and Engineering. The equal contributions of physics, chemistry, and engineering were a great foundation for this young woman with an unquenchable thirst for learning. Her passion for physics started with the discovery of quantum mechanics, where invisible phenomena govern modern technologies. This new passion was coupled with her love for travelling and an increasing interest in Asian cultures and geography, and she moved to Nanyang Technological University in Singapore to complete her Master's thesis in the field of semiconductor nanowires. It was here that she was introduced to the wonderful world of low-dimensional superconductivity, and her journey became filled with novel discoveries and great collaborations.

Autoren/Hrsg.

Ansermet, Diane

Inhaltsverzeichnis

1;Supervisor’s Foreword;7
2;Abstract;8
3;Parts of this thesis have been published in the following journal articles:;9
4;Declaration of Authorship;10
5;Acknowledgements;11
6;Contents;13
7;Abbreviations;17
8;Symbols;19
9;List of Figures;21
10;List of Tables;33
11;Physical ConstantsBohr magneton \mu_{B} = e\hbar /2m_{e} c \approx 9.274 \times 10^{ - 24} J/TBoltzmann constant k_{B} \approx 1.381 \times 10^{ - 23} J/KElectron charge e \approx 1.602 \times 10^{ - 19} CElectron mass m_{e} \approx 9.109 \times 10^{ - 31} kgMagnetic flux quantum \Phi_{0} \equiv \frac{h}{2e} \approx 2.067 \times 10^{ - 15} WbPlanck’s constant h \approx 6.626 \times 10^{ - 34} Js \hbar = h/2\pi \approx 1.054 \times 10^{ - 34} JsSpeed of light c \approx 2.997 \times 10^{8} m/sVacuum permeability \mu_{0} = 4\pi \times 10^{ - 7} N/A2;34
12;1 Superconductivity: History and Motivations;35
12.1;1.1 History;35
12.2;1.2 Motivations: A Fresh Look Towards Functional Superconductors;36
12.3;References;37
13;2 Introduction and Theory;39
13.1;2.1 Superconductivity;39
13.1.1;2.1.1 Experimental Signatures of Superconductivity;39
13.1.2;2.1.2 A Macroscopic Quantum Phenomenon;39
13.1.3;2.1.3 Bardeen–Cooper–Schrieffer Theory;41
13.1.4;2.1.4 Ginzburg–Landau Theory: the Complex Order Parameter;44
13.2;2.2 Superconductivity in Low Dimensions;46
13.2.1;2.2.1 One-Dimensional Phase Fluctuations;47
13.2.2;2.2.2 Quasi-One-Dimensional Superconductors;51
13.2.3;2.2.3 Superconducting Transition in a Quasi-One-Dimensional System;54
13.3;2.3 Josephson Coupling;56
13.3.1;2.3.1 The Josephson Junction and Critical Current;56
13.3.2;2.3.2 The Josephson Energy;57
13.3.3;2.3.3 Internal Josephson Junctions in Low-Dimensional Superconductors;58
13.4;2.4 Disorder and Superconductivity;58
13.4.1;2.4.1 Electron Localization in Three Dimensions;59
13.4.2;2.4.2 Anderson Theorem;61
13.4.3;2.4.3 Metal-Insulator Transition in Two Dimensions;61
13.4.4;2.4.4 New Approaches and Theories;63
13.5;References;64
14;3 Experimental Methods;67
14.1;3.1 The Dilution Refrigerator;67
14.1.1;3.1.1 Mixture Circulation and Condensation;69
14.1.2;3.1.2 Thermal Isolation and Radiation Shielding;72
14.1.3;3.1.3 Mixture Cleaning;75
14.1.4;3.1.4 Mixture Circulation Control and Monitoring;75
14.1.5;3.1.5 Electrical Connections;76
14.1.6;3.1.6 Measurement Probes;78
14.2;3.2 The Variable Temperature Insert;80
14.2.1;3.2.1 Helium Condensation and Circulation;80
14.2.2;3.2.2 Thermal Isolation and Radiation Shielding;81
14.2.3;3.2.3 Helium Gas Cleaning;83
14.2.4;3.2.4 Electrical Connections;83
14.2.5;3.2.5 Measurement Probe;85
14.3;3.3 Superconducting Magnets;85
14.3.1;3.3.1 Superconducting Magnet Materials;86
14.3.2;3.3.2 Stored Energy and Forces in a Magnet;86
14.3.3;3.3.3 Magnet Specifications;87
14.3.4;3.3.4 Operating Modes;90
14.3.5;3.3.5 Electrical Connections;90
14.4;3.4 Helium Recovery and Re-Liquefying Systems;90
14.5;3.5 Electronics;92
14.5.1;3.5.1 Electronics Description;93
14.5.2;3.5.2 Electrical Noise Filtering;95
14.6;3.6 Automated Measurement Systems;96
14.6.1;3.6.1 The Physical Property Measurement System;96
14.6.2;3.6.2 The Magnetic Property Measurement System;98
14.7;3.7 Sample and Contacts Preparation;99
14.7.1;3.7.1 Sample Growth;99
14.7.2;3.7.2 Electrical Contact Preparation;101
14.7.3;3.7.3 Transport Measurement Details;104
14.8;References;104
15;4 The Quasi-One-Dimensional Na2-?Mo6Se6;106
15.1;4.1 Introduction;106
15.2;4.2 The M2-?Mo6Se6 Family;107
15.2.1;4.2.1 The Insulating Compounds;108
15.2.2;4.2.2 The Superconducting Compounds;109
15.2.3;4.2.3 The Intermediate Compound Na2-?Mo6Se6;110
15.3;4.3 Structural Properties;111
15.3.1;4.3.1 Crystal Structure;111
15.3.2;4.3.2 Intrinsic Disorder from Na Vacancies;112
15.4;4.4 Electronic Properties;113
15.4.1;4.4.1 Band Structure;113
15.4.2;4.4.2 Anisotropic Evolution in the M2-?Mo6Se6 Family;117
15.4.3;4.4.3 Anisotropic Random Resistor Network;118
15.5;References;120
16;5 The Electronic Normal State in Na2-?Mo6Se6;123
16.1;5.1 Introduction;123
16.2;5.2 General Observations;123
16.2.1;5.2.1 Intrinsic Disorder in Na2-?Mo6Se6;126
16.3;5.3 Luttinger Liquid in the High Temperature Regime;126
16.3.1;5.3.1 Theory of the Luttinger Liquid;127
16.3.2;5.3.2 Fits to the Luttinger Liquid Model;127
16.3.3;5.3.3 Renormalized Energy Scales in a Disordered System;128
16.4;5.4 Metal-Insulator Transition in the Intermediate Temperature Regime;131
16.4.1;5.4.1 Mechanisms for the Metal-Insulator Transition;131
16.4.2;5.4.2 Fits to the Variable Range Hopping Model;132
16.4.3;5.4.3 Signatures of Anderson Localization;135
16.4.4;5.4.4 Emergence of a Mobility Edge;139
16.5;5.5 Concluding Remarks;141
16.6;References;141
17;6 Superconducting Transition and Pairing Enhancement by Disorder;144
17.1;6.1 Introduction;144
17.2;6.2 Identifying Superconductivity in Na2-?Mo6Se6;145
17.3;6.3 The Superconducting Transition;147
17.3.1;6.3.1 Emergence of 1D Phase-Fluctuating Superconductivity;147
17.3.2;6.3.2 Establishment of a Coherent Superconducting State;149
17.4;6.4 Pairing Enhancement;153
17.4.1;6.4.1 Possible Mechanism for the Enhancement of Superconductivity;158
17.5;6.5 Concluding Remarks;161
17.6;References;162
18;7 Reentrant Phase Coherence by Josephson Coupling;165
18.1;7.1 Introduction;165
18.2;7.2 Reentrant Superconductivity: A Short Overview;166
18.2.1;7.2.1 Reentrant Superconductivity by Josephson Coupling;166
18.2.2;7.2.2 Reentrant Superconductivity by Other Mechanisms;168
18.3;7.3 Experimental Study of the Superconducting State;170
18.3.1;7.3.1 Further Investigation of the 1D Superconducting Transition;170
18.3.2;7.3.2 Observations of Reentrant Phase Coherence;171
18.4;7.4 Analysis;175
18.4.1;7.4.1 Determination of Hc2 and ?(0);175
18.4.2;7.4.2 Estimation of the Filamentary Diameter;176
18.4.3;7.4.3 Mechanism for Reentrant Superconductivity in Na2-?Mo6Se6;177
18.4.4;7.4.4 Calculations of the Josephson Energy;178
18.4.5;7.4.5 Correspondence Between Experimental Data and Calculations;183
18.5;7.5 Concluding Remarks;186
18.6;References;187
19;8 Summary and Outlook;190
19.1;8.1 Summary;190
19.1.1;8.1.1 Project Challenges;192
19.2;8.2 Outlook;193