Photoinduced nonequilibrium response in YBa2Cu3O6.45 and 1T-TaS2 probed by time-resolved terahertz spectroscopy
Nan-Lin Wang (International Center for Quantum Materials, Peking University, Beijing, China)

Ultrafast optical spectroscopy is a powerful tool to investigate the non-equilibrium physics in complex electronic materials. In this talk, I will present our recent time-resolved terahertz spectroscopy study of two different systems: an underdoped YBa2Cu3O6.45 (YBCO) and a charge density wave (CDW) compound 1T-TaS2. I will discuss the aspects of resonant phonon pumping in YBCO and possible transient superconductivity, as derived from the photoexcited nonequilibrium c-axis response. In 1T-TaS2, we differentiate between the dynamical properties of the commensurate CDW state and the stable photoinduced hidden CDW order. Moreover, we also investigate the transient nonequilibrium processes triggered by weak pumping and illustrate that the fluctuating metallic domain walls may develop in the transient states.