Alfred Zong1,2,Yun Cheng3,Lijun Wu4,Qingping Meng4,Wei Xia5,Fengfeng Qi3,Pengfei Zhu3,Xiao Zou3,Tao Jiang3,Yanfeng Guo5,Jasper van Wezel6,Anshul Kogar7,Michael Zuerch1,2,Jie Zhang3,Yimei Zhu4,Dao Xiang3
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Shanghai Jiao Tong University3,Brookhaven National Laboratory4,ShanghaiTech University5,University of Amsterdam6,University of California, Los Angeles7
Alfred Zong1,2,Yun Cheng3,Lijun Wu4,Qingping Meng4,Wei Xia5,Fengfeng Qi3,Pengfei Zhu3,Xiao Zou3,Tao Jiang3,Yanfeng Guo5,Jasper van Wezel6,Anshul Kogar7,Michael Zuerch1,2,Jie Zhang3,Yimei Zhu4,Dao Xiang3
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Shanghai Jiao Tong University3,Brookhaven National Laboratory4,ShanghaiTech University5,University of Amsterdam6,University of California, Los Angeles7
In solids, transient defects are known to generate a variety of hidden orders not accessible in equilibrium, but how defects are formed at the nanometer lengthscale and femtosecond timescale remains unknown. Here, we employ an intense laser pulse to create topological defects in a 2D charge density wave (CDW), and track their morphology and dynamics with ultrafast electron diffraction. Leveraging its high temporal resolution and sensitivity in detecting weak diffuse signals, we discover a dual-stage growth of 1D domain walls within 1 ps, a process not dictated by the CDW amplitude but instead mediated by a nonthermal population of longitudinal optical phonons. Our work provides crucial insights into ultrafast engineering of topological defects based on selective excitation of collective modes, opening avenues for dynamical control of nonequilibrium phases in correlated materials.