  Dynamical materials that capable of responding to optical stimuli have always
been pursued for designing novel photonic devices and functionalities, of which
the response speed and amplitude as well as integration adaptability and energy
effectiveness are especially critical. Here we show ultrafast pulse generation
by exploiting the ultrafast and sensitive nonlinear dynamical processes in
tunably solution-processed colloidal epsilon-near-zero (ENZ) transparent
conducting oxide (TCO) nanocrystals (NCs), of which the potential respond
response speed is >2 THz and modulation depth is ~23% pumped at ~0.7 mJ/cm2,
benefiting from the highly confined geometry in addition to the ENZ enhancement
effect. These ENZ NCs may offer a scalable and printable material solution for
dynamic photonic and optoelectronic devices.
