Excitonic insulator is a coherent electronic phase that results from the formation of a macroscopic population of bound particle-hole pairs - excitons. With only a few candidate materials known, the collective excitonic behavior is challenging to observe, being obscured by crystalline lattice effects. Here we use polarization-resolved Raman spectroscopy to reveal the quadrupolar excitonic mode in the candidate zero-gap semiconductor Ta$_2$NiSe$_5$ disentangling it from the lattice phonons. The excitonic mode pronouncedly softens close to the phase transition, showing its electronic character, while its coupling to non-critical lattice modes is shown to enhance the transition temperature. On cooling, we observe the gradual emergence of coherent superpositions of band states at the correlated insulator gap edge, with strong departures from mean-field theory predictions. Our results demonstrate the realization of a strongly correlated excitonic state in an equilibrium bulk material.
Spontaneously formed excitonic density wave with vortex-antivortex lattice in twisted semiconductor bilayers
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University（南京大学固体微结构物理国家重点实验室和物理系）；Department of Physics, University of Massachusetts（马萨诸塞大学物理系）；Collaborative Innovation Center of Advanced Microstructures, Nanjing University（南京大学先进微结构协同创新中心）；Jiangsu Physical Science Research Center, Nanjing University（南京大学江苏物理科学研究中心）；Hefei National Laboratory（合肥国家实验室）
Spectral properties of strongly correlated multi impurity models in the Kondo insulator regime: Emergent coherence, metallic surface states and quantum phase transitions
Spectral Visualization of Excitonic Pair Breaking at Individual Impurities in Ta2Pd3Te5
Huazhong University of Science and Technology（华中科技大学）；Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology（华中科技大学武汉国家强磁场中心）；Nanjing University（南京大学）；National Laboratory of Solid State Microstructures, Nanjing University（南京大学固态微结构国家重点实验室）；Collaborative Innovation Center for Advanced Microstructures, Nanjing University（南京大学先进微结构协同创新中心）；Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所北京凝聚态物理国家实验室）；University of Chinese Academy of Sciences（中国科学院大学）；Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences（中国科学院大学材料科学与光电技术研究中心）；School of Materials Science and Engineering, Huazhong University of Science and Technology（华中科技大学材料科学与工程学院）；Wuhan Institute of Quantum Technology（武汉量子技术研究院）；Jiangsu Physical Science Research Center, Nanjing University（南京大学江苏物理科学研究中心）
Emergent dynamical Kondo coherence and competing magnetic order in a correlated kagome flat-band metal CsCr6Sb6
ShanghaiTech University（上海科技大学）；Fudan University（复旦大学）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大李政道研究所）；Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所（北京凝聚态物理国家研究中心））；University of Chinese Academy of Sciences（中国科学院大学）；Analytical Instrumentation Center, School of Physical Science and Technology, ShanghaiTech University（上海科技大学分析测试中心）；Shanghai Research Center for Quantum Sciences（上海量子科学研究与创新中心）；ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University（上海科技大学拓扑物理实验室）
Emergent quantum phenomena via phase-coherence engineering in infinite-layer nickelate superconductors
Peking University（北京大学）；University of Electronic Science and Technology of China（电子科技大学）；Renmin University of China（中国人民大学）；ShanghaiTech University（上海科技大学）；Tsinghua University（清华大学）；Institute of Physics Chinese Academy of Sciences（中国科学院物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Songshan Lake Materials Laboratory（松山湖材料实验室）；Beijing Normal University（北京师范大学）；Fudan University（复旦大学）；Hefei National Laboratory（合肥国家实验室）
Tunable Interlayer Charge-transfer States in MoSe$_2$/WS$_2$ Moiré Superlattices
University of California at Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；National Institute for Materials Science（物质材料研究机构）
Emergent Coherence at the Edge of Magnetism: Low-Doped La2-xSrxCuO4+delta Revisited
B. Verkin Institute for Low Temperature Physics and Engineering of the Nat. Acad. of Sciences of Ukraine（乌克兰国家科学院低溫物理與工程B·維爾金研究所）；Smart Materials Group, Mads Clausen Institute, University of Southern Denmark, Sønderborg（南丹麦大学马茨·克拉斯恩学院智能材料组）；National Technical University «Kharkiv Polytechnic Institute», Kharkiv, Ukraine（乌克兰哈尔科夫国立技术大学（哈尔科夫理工学院））
Observation of two-component exciton condensates in an excitonic insulator
University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；National Institute for Materials Science（物质材料研究机构）；University of Texas at Austin（德克萨斯大学奥斯汀分校）；Kavli Energy NanoScience Institute, University of California Berkeley and Lawrence Berkeley National Laboratory（加州大学伯克利分校与劳伦斯伯克利国家实验室卡弗里能源纳米科学研究所）
