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【摘要】

The discovery of quantum materials has led to significant advances in condensed matter physics. Conventional fields such as magnetism and superconductivity have been revolutionized by the concept of topology, which provides an ideal platform for realizing novel physical phenomena. To deepen our understanding of quantum phenomena, it is crucial to search for different quantum phases and find ways to control their properties on demand. In this talk, I will present my studies on the control of low-dimensional quantum materials under equilibrium and nonequilibrium conditions.
First, I will discuss the engineering of topological insulator phases in quasi-1D bismuth halides using their stacking sequences. Among different types of topological insulators (TIs), strong TIs have been demonstrated immediately after their theoretical prediction by observing the surface states through photoemission spectroscopy. In contrast, weak and higher-order TIs remained elusive due to the experimental difficulties in detecting their boundary states. Here, I will show that quasi-1D bismuth halides provide an ideal playground for studying and manipulating these topological phases. Using a high-resolution laser and a synchrotron-based nanobeam, I have found evidence for weak and higher-order TI phases in bismuth halides depending on their stacking sequences.
Second, I will discuss the ultrafast optical manipulation of a layered antiferromagnet. Here, I have explored the possibility of Floquet engineering, where a time-periodic electromagnetic field is applied to control the electronic and magnetic properties of materials. I applied white light-based broadband transient reflection spectroscopy to the layered antiferromagnet MnPS3 and observed coherent phonon generation after Floquet driving. The Floquet-based picture of coherent phonon generation will be discussed.
[1] R. Noguchi et al., Nature 566, 518–522 (2019).
[2] R. Noguchi et al., Nat. Mater. 20, 473 (2021).
[3] R. Noguchi et al., arXiv:2301.07158.
[4] R. Noguchi, D. Hsieh et al., in preparation.