USTC has made important progress in the field of cage mesh superconductor research
The research team composed of Chen Xianhui, Wu Tao and Wang Zhenyu from Hefei National Research Center for micro scale material science, University of science and technology of China, School of physics and Key Laboratory of strong coupling quantum material physics, Chinese Academy of Sciences, recently made important progress in the research of cage mesh superconductors. The research team observed in the cage superconductor csv3sb5 that the charge density wave sequence evolved into an electronic nematic phase described by the three state Potts model at low temperature. The discovery of this nematic phase not only provided important experimental evidence for understanding the abnormal competition between charge density wave and superconductivity in the cage superconductor, It also provides a new research direction for the further study of intertwined orders closely related to unconventional superconductivity in correlated electron systems. Relevant research results were published online in Nature magazine in the form of "accelerated article preview" on February 9 under the title of "charge density wave driven electronic neutrality in a kagome superconductor".
Figure: physical diagram of electron nematic sequence and superconductivity caused by triple modulated charge density waveguide in cage structure superconductor
Electron nematic phase is a kind of electron ordered state produced by the spontaneous breaking of the rotational symmetry of electron degrees of freedom. It widely exists in electronic systems such as high temperature superconductors and quantum Hall insulators. There is a close relationship between electron nematic phase and high temperature superconductivity. It is considered as an interleaving sequence associated with high temperature superconductivity. It is a major scientific problem and research hotspot in the theoretical research of high temperature superconductivity. Exploring superconducting material systems with new structures and further studying the relationship between superconductivity and various interleaving sequences is an important research direction in the current field. One kind of systems that have attracted much attention is two-dimensional cage structure. The theory predicts that near the van Hove singularities doping, the two-dimensional cage system can show novel superconductivity and rich electronic ordered states, but there has been a lack of suitable material system to realize its related physics for a long time. In recent years, the discovery of cage superconductor csv3sb5 provides a new research system for the exploration of this direction. In the previous research, the superconductivity research team of China University of science and technology has successfully revealed the charge density wave state of triple-q in the system (Phys. Rev. X 11, 031026 (2021)), and the abnormal competition relationship between charge density wave and superconductivity under pressure (NAT. Common. 12, 3645 (2021)).
On this basis, the research team fully combined the three experimental technologies of scanning tunneling microscope, nuclear magnetic resonance and elastic resistance to conduct a detailed study on the evolution of charge density wave state in csv3sb5. They found that before the system entered the superconducting state, the triple modulated charge density wave state would further evolve into a thermodynamically stable electron nematic phase, and the transition temperature was determined to be about 35 Kelvin. The electron nematic phase is different from the electron nematic phase previously observed in high temperature superconductors: the electron nematic phase in high temperature superconductors is ising type nematic phase with Z2 symmetry; The electron nematic phase found in cage superconducting csv3sb5 has Z3 symmetry, which is theoretically described by the three state Potts model, so it is also called "Potts" nematic phase. Interestingly, this new electronic nematic phase has recently been observed in bilayer corner graphene system.
These findings not only reveal a new type of electron nematic phase in cage superconductors, but also provide experimental evidence for understanding the competition between superconductivity and charge density wave in such systems. Previous scanning tunneling spectroscopy studies have shown that there may be paired density wave state (PDW) formed by the interweaving of superconductivity and charge density wave order in csv3sb5 system. The electron nematic sequence found above the superconducting transition temperature can be understood as an interleaving sequence related to PDW. This research result also provides important clues and ideas for understanding PDW in high temperature superconductors. How to understand the formation mechanism of superconductivity and its interleaving order in cage superconductors needs further experimental and theoretical research.
Nie Linpeng and sun Fulu, doctoral students of Hefei National Research Center for micro scale material science, and Ma Wanru, doctoral student of the school of physics, are the co first authors of the paper, and Professor Chen Xianhui, Professor Wu Tao and Professor Wang Zhenyu are the co corresponding authors of the article. The relevant work has been supported by the Ministry of science and technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences, the guidance project of Anhui Province and the innovation team project of the University.
Paper link:https:// www.nature. com/articles/s41586-022-04493-8
