The subject of low-energy excitations has evolved since two-level-tunneling systems were first proposed 50 years ago. Initially they were used to explain the common anomalous properties of oxide glasses and polymers; now the subject includes a wide range of other materials containing disorder: amorphous semiconductors and metals, doped- mixed- and quasi-crystals, surface adsorbates, ... and topics such as dephasing of quantum states and interferometer noise. A fairly simple empirical description using a remarkably small range of parameters serves well to describe the effect of these excitations, but the structures causing these effects are known in only a few materials and the reasons for their similarity across disparate materials has only been qualitatively addressed.This book provides a unified, comprehensive description of tunneling systems in disordered solids suitable for graduate students/researchers wishing an introduction to the field. Its focus is on the tunneling systems intrinsic to glassy solids. It describes the experimental observations of 'glassy' properties, develops the basic empirical tunneling model, and discusses the dynamics changes on cooling to temperatures where direct excitation interactions become important and on heating to where tunneling gives way to thermal activation. Finally, it discusses how theories of glass formation can help us understand the ubiquity of these excitations.The Development of the basic tunneling model is the core of the book and is worked out in considerable detail. To keep the total within bounds of our expertise and the readers' patience, many related experimental and theoretical developments are only sketched out here; the text is heavily cited to allow readers to follow their specific interests in much more depth.
Author(s): Richard B. Stephens, Xiao Liu
Publisher: World Scientific Publishing
Year: 2021
Language: English
Pages: 417
City: Singapore
Contents
Foreword
Preface
1. Introduction and Scope
1.1. A priori expectations
1.2. Glasses cooled from liquids vs. other disorder
1.3. Modeling glassy systems
1.4. Plan of the book
2. Basic Glass Concepts
2.1. Glass (meta)stability
2.2. Liquid–solid transition — inhomogeneity — glass transition, Kauzmann paradox
2.3. Non-glass disorder: Physical and Chemical Vapor Deposition, oxidation, polymerization, etc.
2.4. Vibrational spectra
2.4.1. Debye model
2.4.2. Intermediate temperatures
2.4.3. Lower temperatures
2.5. Impurity specific heat
3. Common Properties of Disordered Materials
3.1. Normalizing to the Debye model
3.2. Excess density of states
3.3. Coupling to thermal phonons
3.4. Coupling to acoustic waves
3.5. Anharmonicity
3.6. Measurement time
3.7. Saturation
3.8. Coupling to EM fields
3.9. Coupling to static magnetic fields
3.10. Coupling to dopant molecules
3.11. Coupling to qubits
3.12. Coupling to electrons
3.13. Summary
4. Standard Tunneling Model
4.1. Previously known tunneling systems
4.2. Standard two-level tunneling model (STM)
4.3. Tunnel system — phonon interactions
4.3.1. TLS distribution
4.3.2. T1 — population equilibration time
4.3.3. T2 — phase coherence time
4.4. STM — specific heat
4.4.1. Short-time specific heat measurements
4.4.2. Slow heat flow
4.5. STM — thermal conductivity
4.6. STM — phonon coupling-steady state
4.6.1. Internal friction, sound speed — I
4.6.2. Internal friction, sound speed — II
4.6.3. Saturation
4.6.4. STM — anharmonicity?
4.7. STM — phonon coupling — short-time
4.7.1. Saturation recovery
4.7.2. Hole burning/spectral diffusion
4.7.3. Phonon echoes — relaxation rates
4.7.4. Probing individual TLS — non-resonant
4.8. STM — electron interactions
4.9. STM — universality and uniformity
4.10. STM — temperature limits
4.10.1. Low-temperature limits
4.10.2. High-temperature limits
4.11. Consequence of the STM description
5. Standard Tunneling Model Extensions
5.1. TLS–TLS pairs
5.2. Strong TLS–TLS interaction
5.3. Fine tuning model parameters
5.3.1. Superlinear specific heat
5.3.2. TLS parameter correlations
5.3.2.1. Strict proportionality
5.3.2.2. Proportionality in range
5.3.2.3. Correlation consequence
5.4. Soft potential model
5.5. Interactions with nuclear quadrupoles
5.6. Multi-well, multi-barrier tunneling states
5.7. Reduced dimensions
5.7.1. T1,d: Phonon spectrum modification
5.7.2. T2,d: Reduced TLS–TLS interactions
5.8. Summary
6. Manipulating Tunneling States
6.1. Density
6.1.1. Annealing
6.1.2. Pressure
6.1.3. Neutron irradiation
6.2. Disorder modification
6.2.1. Added strain
6.2.2. Irradiation changes in glasses
6.2.3. Sidestepping Tg: Non-glass amorphous solids
6.2.3.1. Polymerization, cross-linking
6.2.3.2. Oxidation
6.2.3.3. Vapor deposition
6.2.3.4. Ultra-stable films
6.3. Local atomic connectivity
6.4. Limited dimensions
6.5. Disorder in crystals
6.5.1. Complex crystals
6.5.2. Susceptible crystalline structures
6.5.2.1. Quasicrystals
6.5.2.2. Crystals with diffusionless phase transitions
6.5.2.3. Crystals with mobile components
6.5.3. Defective crystals
6.5.3.1. Irradiation of crystals
6.5.3.2. Strained crystalline metals
6.5.4. Extrinsic TLS
6.5.4.1. Dopants, contamination
6.5.4.2. Mixed crystals
6.6. Summary — TLS manipulation
6.6.1. Summary-glasses
6.6.2. Summary-crystallinity
7. Forming TLS
7.1. Cooling a liquid
7.2. Structural models
7.2.1. Atomistic models
7.2.2. Stability models
7.3. Dynamics models
7.3.1. Mode coupling theory
7.3.2. Random first-order transition
7.4. Summary
8. Higher Temperatures: Thermal Activation and the Boson Peak
8.1. Thermal activation extension of the STM
8.1.1. Empirical extension to Tg
8.2. Experimental observations and empirical fits
8.2.1. The boson peak
8.2.1.1. Specific heat
8.2.1.2. Inelastic scattering
8.2.1.3. Other BP correlations
8.2.2. κ(T ) plateau
8.3. Dynamic models
8.3.1. Packed sphere models
8.3.2. Introducing disorder
8.3.3. Introducing defects
8.4. Theoretical frameworks and RFOT
8.4.1. Random First Order Transition Theory
8.5. Summary
9. Effects on Low Temperature Technologies
9.1. Cryomaterials needs
9.2. Interferometers: LIGO
9.3. Mechanical resonators
9.4. Electromagnetic resonators
9.5. Josephson junctions, qubits
9.6. Quantum communications
10. Conclusions — Future Directions
10.1. Ultra-stable films
10.2. Tuning connectivity
10.3. Final musings on the ‘universality’ of C
Appendix A: Detailed Dynamics Derivations
A.1. Setup
A.2. TLS dynamics
A.3. Phonon–TLS interactions
A.4. Electron–TLS interactions
Appendix B: Symbol List
Bibliography
