Recently, the Soft Matter and Active Matter Collaborative Research Group of Shanghai Jiao Tong University (Matteo Baggioli Group of Wilczek Quantum Center and Jie Zhang Group of Institute of Natural Sciences / School of Physics and Astronomy) made important progress in the study of local vibration of active particulate matter. Based on the experiment of active Brownian particle system, the research group confirmed the local vibration of strings, and its corresponding zero group velocity dispersion relation predicted two years ago. This study is of great significance for understanding the singularity of the intrinsic vibration of amorphous solids, which is a mystery left to be solved in the last century.
The twisted bilayer graphene (TBG) system is one of the important discoveries in condensed matter physics in recent years. It has become an extremely rich platform for studying quantum many-body physics. Especially at a specific twist angle, the so-called “magic angle” (approximately 1.05 degrees), TBG undergoes a superconducting phase transition. Although the origin of exotic superconductivity in TBG remains a controversial topic, it is generally believed that the flat-band effect plays an essential role. However, since TBG is not a stable configuration at the magic angle, it is often difficult to accurately prepare magic-angle graphene experimentally. Experiments have observed that when the twist angle deviates from the magic angle by 0.1 degrees, the superconducting phase disappears. This instability has limited extensive research on superconducting properties in TBG.
In this study, the researchers proposed a new method, namely, using quantum fluctuations in a chiral microcavity to engineer the band structure of TBG, so that TBG can form a flat band beyond the magic angle. The physical picture is that the chiral microcavity breaks time-reversal symmetry, and the vacuum quantum fluctuations in the cavity inherit the characteristics of time-reversal symmetry breaking. The time-reversal symmetry broken quantum fluctuations can induce energy gaps in the band structure, leading to a significant impact on the band flatness near the magic angle. By controlling the effective mode volume of the chiral microcavity, one can effectively tune the coupling strength of electron-photon interaction, achieving precise control of the band structure and even topological properties of the system. This work is based on the previous studies on the quantum atmospheric effect and the chiral vacuum molecule selection effect.
A cartoon of the idea behind the identification of topological defects in the vibrational modes of glasses.
Professor Matteo Baggioli (STJU and WQC) summarizes the recent breakthroughs in the search of topological defects in amorphous materials in a News and Views commentary for Nature Communications.
