Electronic Band Structure Engineering and Ultrafast Dynamics of Dirac Semimetals

This book highlights the doctoral research of the author on electronic band structure engineering and ultrafast dynamics of Dirac semimetals. Dirac semimetals exhibit unique electronic band structure and novel physical properties with rich light-matter interaction, which inspires a wide range of potential applications. Enabling band engineering and revealing ultrafast dynamics of Dirac semimetals is therefore important. In the research work covered by the book, the first ultrafast time- and angle-resolved photoemission spectroscopy with tunable probe photon energy is developed, providing new opportunities for exploring ultrafast dynamics in 3D quantum materials. Using the spectroscopy, the author investigates the band structure engineering and ultrafast dynamics of Dirac semimetals, realizing the long-sought-after chiral symmetry breaking in a Kekulé-ordered graphene with flat band and revealing the ultrafast dynamics of Dirac fermions in 3D Dirac semimetal for the first time. The work advances the research of the electronic structure of Dirac semimetals in two aspects. Firstly, it identifies the Kekulé-ordered graphene as a new system for exploring chiral symmetry breaking- related physics and flat band- induced instability, providing a very rare system to investigate their interplay. Secondly, it solves the long-standing challenge of directly visualizing the non-equilibrium electronic structure of 3D Dirac semimetal and opens up new opportunities for exploring the light-matter interaction in 3D quantum materials, especially the light-induced topological phase transitions in 3D topological materials.

Introduction.- Experimental Techniques.- Development of Novel Trarpes With Tunable Probe Photon Energy for 3D Quantum Materials.- Chiral Symmetry Breaking in Kekulé-ordered Graphene.- Coexistence of Flat Band and Kekulé Order.

Changhua Bao received his B.S. in Mathematics and Physics in 2016 and Ph.D. in Physics in 2022 from the Department of Physics, Tsinghua University, China. His research focuses on the novel electronic structure and light-matter interaction in two-dimensional and topological materials by utilizing state-of-the-art angle-resolved photoemission spectroscopy (ARPES) including time- and spatial-resolved ARPES. He has been awarded Outstanding Scholarship for graduate students (top 0.1%) in Tsinghua university (2021), Young Scientist Prize in Recent Progress in Graphene and Two-dimensional Materials Research Conference (2019) and China's National Scholarship for Graduate Students (2018).