狄拉克半金属具有独特的电子能带结构、丰富光与物质相互作用诱导的新奇物理性质和潜在应用前景，研究狄拉克半金属中的电子能带结构调控和超快电子动力学具有重要意义。本书介绍了具有可调探测光子能量的超快时间分辨角分辨光电子能谱的研制，为探索三维量子材料中的超快电子动力学提供了新的机遇。通过利用该电子能谱技术，研究了狄拉克半金属的电子能带结构调控和超快电子动力学，其中包括在具有平带电子结构的凯库勒石墨烯中实现了手征对称性破缺这一重要物理效应；揭示了三维狄拉克费米子的超快动力学过程。
本书从两个方面推动了狄拉克半金属的电子结研究。首先，发现了凯库勒石墨烯这一新材料体系，为探索手征对称性破缺相关物理和平带诱导的电子态失稳及两者之间的相互作用提供了一个非常难得的研究系统。其次，解决了直接观测三维狄拉克半金属非平衡电子结构研究中长期存在的实验挑战，并为探索三维量子材料中的光与物质相互作用，特别是三维拓扑材料中光诱导的拓扑相变提供了新的机遇。

1 Introduction
1.1 Overview of Dirac Semimetal
1.1.1 2D Dirac Semimetal
1.1.2 3D Dirac Semimetal
1.2 Intriguing Light-Matter Interaction in Dirac Semimetal
1.2.1 Ultrafast Dynamics and Population Inversion
1.2.2 Floquet Engineering in Dirac Semimetal
References
2 Experimental Techniques
2.1 Angle-Resolved Photoemission Spectroscopy
2.1.1 Basic Principles
2.1.2 Instruments
2.2 Time-and Angle-Resolved Photoemission Spectroscopy
2.2.1 Basic Principles
2.2.2 Special Technical Considerations
References
3 Development of Novel TrARPES with Tunable Probe Photon Energy for 3D Quantum Materials
3.1 Research Motivation
3.2 TrARPES with Tunable Probe Photon Energy
3.2.1 Experimental Setup
3.2.2 Tunable Probe Photon Energy
3.2.3 Considerations for the Time Resolution
3.2.4 TrARPES Functionality
3.3 Conclusions
References
4 Chiral Symmetry Breaking in Kekulé-Ordered Graphene
4.1 Research Motivation
4.2 Experimental Evidence of Chiral Symmetry Breaking
4.2.1 Preparation of Kekulé-Ordered Graphene
4.2.2 Evidence of CSB 1: Band Gap Opening
4.2.3 Evidence of CSB 2: Kekulé-O Order
4.2.4 Evidence of CSB 3: Chirality Mixing
4.3 Conclusion
References
5 Coexistence of Flat Band and Kekulé Order
5.1 Research Motivation
5.2 Extremely High Doping Level
5.3 Strong el-ph Coupling
5.4 Co-development of Flat Band and Kekulé Order
5.5 Conclusion
References
6 Dirac Fermion Cooling in 3D Dirac Semimetal Cd3As2
6.1 Research Motivation
6.2 Revealing the 3D Dirac Cone
6.3 Photoexcited Carrier Dynamics
6.4 Ultrafast Thermodynamics
6.5 Population Inversion
6.6 Conclusion
References
7 Summary and Prospects
References