"Evidence for topological defects in a photoinduced phase transition"

Alfred Zong : Anshul Kogar, Ya-Qing Bie, Timm Rohwer, Changmin Lee, Edoardo Baldini, Emre Ergeçen, Mehmet B. Yilmaz, Byron Freelon, Edbert J. Sie, Hengyun Zhou, Joshua Straquadine, Philip Walmsley , Pavel E. Dolgirev, Alexander V. Rozhkov, Ian R. Fisher, Pablo Jarillo-Herrero, Boris V. Fine and Nuh Gedik; Nature Physics, 10/15/18.

Additional Authors: Anshul Kogar, Ya-Qing Bie, Timm Rohwer, Changmin Lee, Edoardo Baldini, Emre Ergeçen, Mehmet B. Yilmaz, Byron Freelon, Edbert J. Sie, Hengyun Zhou, Joshua Straquadine, Philip Walmsley , Pavel E. Dolgirev, Alexander V. Rozhkov, Ian R. Fisher, Pablo Jarillo-Herrero, Boris V. Fine and Nuh Gedik

Abstract:

Upon excitation with an intense laser pulse, a symmetrybroken ground state can undergo a non-equilibrium phase transition through pathways different from those in thermal equilibrium. The mechanism underlying these photoinduced phase transitions has long been researched in the study of condensed matter systems1, but many details in this ultrafast, non-adiabatic regime still remain to be clarified. To this end, we investigate the light-induced melting of a unidirectional charge density wave (CDW) in LaTe3. Using a suite of time-resolved probes, we independently track the amplitude and phase dynamics of the CDW. We find that a fast (approximately 1 picosecond) recovery of the CDW amplitude is followed by a slower re-establishment of phase coherence. This longer timescale is dictated by the presence of topological defects: long-range order is inhibited and is only restored when the defects annihilate. Our results provide a framework for understanding other photoinduced phase transitions by identifying the generation of defects as a governing mechanism.