Pohang University of Science and Technology

报告人简介：

Bumjoon Kim is a Professor in the Department of Physics at Pohang University of Science and Technology (POSTECH), where he also serves as a leading researcher in condensed matter physics, focusing on strongly correlated electron systems and spin-orbital dynamics. From 2017 to 2023, he was an Associate Director at the Institute for Basic Science's Center for Low-Dimensional Electronic Systems. Previously, he held prominent research positions, including Group Leader at the Max Planck Institute for Solid State Research and Assistant Physicist at Argonne National Laboratory. His research interests center on the interplay between electron correlation and spin-orbit coupling in low-dimensional quantum materials. His pioneering work has led to the identification of novel quantum states, such as the Jeff=1/2 Mott state in iridates, and significant contributions to the understanding of emergent phenomena in spin-orbit Mott insulators. He employs advanced techniques like resonant inelastic X-ray scattering (RIXS) and angle-resolved photoemission spectroscopy (ARPES) to probe the electronic structure and dynamics of these materials. Among his many accolades are the Next-Generation Scientist Award from the Korean Academy of Science and Technology (2022) and the Brian R. Coles Prize from the International Conference on Strongly Correlated Electron Systems (2013). His recent work includes studies on spin nematic orders in quantum antiferromagnets and the search for next-generation high-temperature superconductors.

报告摘要：

Chirality is a ubiquitous phenomenon in which a symmetry between left- and right-handed objects is broken, examples in nature ranging from subatomic particles and molecules to living organisms. However, mechanisms that lead to chirality in condensed matter systems remain poorly understood. In this talk, I will discuss on a novel mechanism of chiral charge density wave formation in the transition-metal dichalcogenide 1T-TiSe2. Based on a rigorous symmetry analysis, we show that charge density modulations and ionic displacements, which transform as a continuous scalar field and a vector field on a discrete lattice, respectively, follow different irreducible representations of the space group, despite the fact that they propagate with the same wave-vectors and are strongly coupled to each other. This charge-lattice symmetry frustration is resolved by further breaking of all symmetries not common to both sectors through induced lattice distortions, thus leading to chirality. Our theory is verified using Raman spectroscopy and inelastic x-ray scattering, which reveal that all but translation symmetries are broken at a level not resolved by state-of-the-art diffraction techniques.

邀请人：李源（yuan.li@iphy.ac.cn）

联系人：胡颖（8264 9361）