Defect-mediated nucleation of a charge density wave in rare-earth tritelluride

Understanding the origin of phase transitions, as well as how distinct phases interact, remains the central task of condensed matter physics. One of the physical systems that provides platforms for studying phase transitions and competitions is the charge density wave (CDW), an emergent order typically resulting from electron-phonon couplings. Though the origin of CDW phases in some material systems could be approximately explained by Fermi surface nesting (FSN) or electron-phonon coupling theory, many other CDW phase transitions in exotic materials defy the paradigm, making CDW materials interesting for the search for the microscopic origin of a phase transition. One example is rare-earth tritelluride, a family of CDW materials with two competing CDW orders. While the dominant CDW formation falls into the well-known electron-phonon coupling regime, the formation mechanism of the subdominant CDW remains enigmatic. In this work, deploying time-and-angle-resolved photoemission spectroscopy (trARPES), we unveil a novel mechanism of nucleation-like growth that potentially drives the enigmatic secondary CDW phase transition in rare-earth tritellurides by analyzing the vastly different recovery behaviors of different CDW orders upon light excitation. Our work not only demystifies a new type of CDW formation mechanism in the specific material system but also establishes a non-equilibrium framework for comprehending phase transitions in quantum materials where phase competition is involved.