Observation of quantum effects in charge nonequilibrium states with polarization analysis

다국어 초록 (Multilingual Abstract)

This dissertation demonstrates experimental results of charge-nonequilibrium states in various quantum materials using the laser microscopy technique. Optical excitations and electrical bias realize the nonequilibrium states in this dissertation. The excitation states are measured by optical methods, e.g. magneto-optical Kerr effect (MOKE), electro-optic effect, terahertz pulse, thermoreflectance, and so on. Magnetism, topological effect, pseudo-hydrodynamic phenomena, and heat transport effects are investigated as target phenomena. For magnetic systems, I utilize the electrical/optical excitation method to perturb the magnetic states and successfully observed the spin/orbital Hall effect and related phenomena. For the topologically non-trivial system, the current-induce nonlinear Kerr rotation effect and Dirac surface states are also observed in a Weyl semimetal and a topological insulator, respectively. I also conduct charge distribution mapping experiment and I study a pseudo-hydrodynamic behavior in a semimetal. In aspect of heat transports, nanoscale heat transfer effect through atomically thin film is investigated. I also suggest a methodology of optical heat mapping with millikelvin resolution. I hope that my research results can offer useful optical methodologies and valuable information to the field of condensed matter physics.

국문 초록 (Abstract)

이 논문은 레이저 분광 기술을 사용하여, 다양한 양자 물질에서의 전하-비평형 상태에 대한 실험 결과를 보여준다. 이 논문에서는 광-여기 및 전기 바이어스를 이용해 비평형 상태를 만들고, 여기된 상태는 레이저 분광 방법으로 측정된다. 이 논문에서 쓰인 광학적 방법은 자기 광학 커 효과(MOKE), 전기 광학 효과, 테라헤르츠 펄스, 열반사율 등이 있다. 자기, 위상 효과, 유사 유체 역학 현상 및 열 전달 효과를 대상 현상으로 조사합니다. 자기 시스템의 경우 전기/광학 방법을 사용하여 자기 상태를 들뜬 상태로 만들었으며, 스핀/궤도 홀 효과 및 관련 현상을 성공적으로 관찰했다. 위상 물질의 경우 전류에 의해 유도된 비선형 커 효과와 디락 표면 상태를 측정하였다. 또한 전하 분포 매핑 실험을 수행하고 반금속의 유사-유체 역학 거동을 연구하였다. 열전달 측면에서는 원자층 박막을 통한 나노미터 수준에서의 열전달 효과를 연구했다. 또한 밀리켈빈 분해능의 광학 열 매핑 방법을 제안하였다. 이 연구 결과가 응집물질물리학 분야에 유용한 광학적 방법론과 귀중한 정보를 제공할 것이라 생각한다.

목차 (Table of Contents)

• Abstract 1
• Chapter I. INTRODUCTION 2
• 1.1. Motivations 2
• 1.1.1. Spin/orbitronics 2
• 1.1.2. Topological effects 3
• 1.1.3. Charge mapping and hydrodynamics 3
• 1.1.4. Heat transport 4
• 1.2. Outlines 4
• 1.3 References 7
• Chapter II. EXPERIMENTAL METHODS 10
• 2.1. Magneto-optical Kerr effect 10
• 2.1.1. Phenomenological description 10
• 2.1.2. Microscopic origin 12
• 2.2. References 13
• 2.3. Figures 14
• Chapter III. DIRECT DETECTION OF THE ORBITAL HALL EFFECT 15
• 3.1. Introduction 15
• 3.2. Experimental method 16
• 3.3. Direct measurement of orbital angular momentum 17
• 3.4. Orbital-torque measurement 21
• 3.5. Conclusion 22
• 3.6. References 23
• 3.7. Figures 28
• 3.8. Supplementary information 33
• 3.9. Supplementary references 86
• 3.10. Supplementary figures 90
• Chapter IV. DAMPING OF SPIN WAVES IS A SOFT MAGNET 111
• 4.1. Introduction 111
• 4.2. Experimental method 113
• 4.3. Results and discussion 114
• 4.4. Conclusion 116
• 4.5. References 118
• 4.6. Figures 121
• Chapter V. TIME-RESOLVED MAGNETIZATION VECTORS DRIVEN BY PULSED SPIN-ORBIT TORQUE 125
• 5.1. Introduction 125
• 5.2. Experimental method 126
• 5.3. Results and discussion 128
• 5.4. Conclusion 132
• 5.5. References 133
• 5.6. Figures 136
• Chapter VI. PHOTOCARRIER DYNAMICS IN A TOPOLOGICAL INSULATOR 139
• 6.1. Introduction 139
• 6.2. Experimental method 140
• 6.3. Results and discussion 143
• 6.4. Conclusion 148
• 6.5. References 150
• 6.6. Figures 152
• Chapter VII. NONLINEAR OPTICAL HALL EFFECT 156
• 7.1. Introduction 156
• 7.2. Experimental method 159
• 7.3. Results and discussion 161
• 7.4. Conclusion 166
• 7.5. References 166
• 7.6. Figures 169
• 7.7. Supplementary information 173
• 7.8. Supplementary references 188
• 7.9. Supplementary figures 189
• Chapter VIII. OPTICAL DETECTION OF CHARGE ACCUMULATION 196
• 8.1. Introduction 196
• 8.2. Experimental method 197
• 8.3. Results and discussion 199
• 8.4. Conclusion 202
• 8.5. References 203
• 8.6. Figures 205
• Chapter IX. PSEUDO-HYDRODYNAMICS 208
• 9.1. Introduction 208
• 9.2. Experimental method 209
• 9.3. Results and discussion 214
• 9.4. Conclusion 217
• 9.5. References 218
• 9.6. Figures 220
• 9.7. Supplementary information 224
• 9.8. Supplementary references 232
• 9.9. Supplementary figures 234
• Chapter X. STRONG PHONON SCATTERING THROUGH AN ATOMICALLY THIN FILM 242
• 10.1. Introduction 242
• 10.2. Experimental method 244
• 10.3. Results and discussion 246
• 10.4. Conclusion 251
• 10.5. References 252
• 10.6. Figures 254
• Chapter XI. OPTICAL THERMOMETRY WITH POLARIZATION MICROSCOPY 259
• 11.1. Introduction 259
• 11.2. Experimental method 260
• 11.3. Results and discussion 262
• 11.4. Conclusion 264
• 11.5. References 265
• 11.6. Figures 267
• Chapter XII. CONCLUSION 271