  Exotic phenomenon can be achieved in quantum materials by confining
electronic states into two dimensions. For example, relativistic fermions are
realised in a single layer of carbon atoms, the quantized Hall effect can
result from two-dimensional (2D) systems, and the superconducting transition
temperature can be enhanced significantly in a one-atomic-layer material.
Ordinarily, 2D electronic system can be obtained by exfoliating the layered
materials, growing monolayer materials on substrates, or establishing
interfaces between different materials. Herein, we use femtosecond infrared
laser pulses to invert the periodic lattice distortion sectionally in a
three-dimensional (3D) charge density wave material, creating macroscopic
domain walls of transient 2D ordered electronic states with exotic properties.
The corresponding ultrafast electronic and lattice dynamics are captured by
time- and angle-resolved photoemission spectroscopy and MeV ultrafast electron
diffraction. Surprisingly, a novel energy gap state, which might be a signature
of light-induced superconductivity, is identified in the photoinduced 2D domain
wall near the surface. Such optical modulation of atomic motion is a new path
to realise 2D electronic states and will be a new platform for creating novel
phases in quantum materials.
