In low-dimensional systems with strong electronic correlations, the application of an ultrashort laser pulse often yields novel phases that are otherwise inaccessible. The central challenge in understanding such phenomena is to determine how dimensionality and many-body correlations together govern the pathway of a non-adiabatic transition. To this end, we examine a layered compound, 1T-TiSe$_2$, whose three-dimensional charge-density-wave (3D CDW) state also features exciton condensation due to strong electron-hole interactions. We find that photoexcitation suppresses the equilibrium 3D CDW while creating a nonequilibrium 2D CDW. Remarkably, the dimension reduction does not occur unless bound electron-hole pairs are broken. This relation suggests that excitonic correlations maintain the out-of-plane CDW coherence, settling a long-standing debate over their role in the CDW transition. Our findings demonstrate how optical manipulation of electronic interaction enables one to control the dimensionality of a broken-symmetry order, paving the way for realizing other emergent states in strongly correlated systems.
Persistence of charge ordering instability to Coulomb engineering in the excitonic insulator candidate TiSe$_2$
University of St Andrews（圣安德鲁斯大学）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Universität Hamburg（汉堡大学）；STFC Central Laser Facility, Research Complex at Harwell（STFC 哈韦尔研究综合体中央激光设施）；Bremen Center for Computational Materials Science（不来梅计算材料科学中心）
Odd-to-Even-Layer Switch of Spontaneous Excitonic State in $\rm{TiSe_{2}}$ Thin Films
National Laboratory of Solid State Microstructure, School of Physics, Nanjing University（南京大学固体微结构物理学院国家实验室）；Jiangsu Physical Science Research Center, Nanjing University（南京大学江苏省物理科学研究中心）；Hefei National Laboratory（合肥国家实验室）；Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area（粤港澳大湾区量子科学中心）；State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University（清华大学物理系低维量子物理国家重点实验室）；Department of Physics and Guangdong Basic Research Center of Excellence for Quantum Science, Southern University of Science and Technology（南方科技大学物理系广东省量子科学基础研究中心）
Direct Evidence for Robust Bulk Band Gap Across the Charge Density Wave Transition in TiSe2
Xiamen University Malaysia（厦门大学马来西亚分校）；University of Connecticut（康涅狄格大学）；SRM University - AP（SRM大学-安得拉邦校区）；University of Nebraska-Lincoln（内布拉斯加大学林肯分校）；University of New Hampshire（新罕布什尔大学）；Brookhaven National Lab（布鲁克海文国家实验室）
Electron-phonon-dominated charge-density-wave fluctuations in TiSe$_2$ accessed by ultrafast nonequilibrium dynamics
Université de Bordeaux（波尔多大学）；CEA（法国原子能和替代能源委员会）；CELIA（激光与相互作用中心实验室）；Universität Würzburg（维尔茨堡大学）；Institute of Physics, 10000 Zagreb（萨格勒布物理研究所）；European Theoretical Spectroscopy Facility（欧洲理论光谱设施）；Institut National de la Recherche Scientifique（国家科学研究学院）；University of West Bohemia（西波希米亚大学）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）
Ultrafast Stiffening of the Lattice Potential and Metastable State Formation in 1$T$-TiSe$_2$
Central South University（中南大学）；Hunan University of Science and Technology（湖南科技大学）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）；Uppsala University（乌普萨拉大学）
