Fig. 1: Transient hexatic state observed by high-coherence ultrafast nanobeam diffraction.
From: Light-induced hexatic state in a layered quantum material
a, Schematic of the Ultrafast TEM. A specimen is excited using femtosecond laser pulses (red). The resulting transient disorder is captured by ultrashort electron pulses (green) generated via linear photoemission (blue) from a field-emitter cathode. b, Microscopic mechanism of two-dimensional (2D) thermal melting via a hexatic phase, involving the step-wise unbinding of topological defects (KTHNY theory). Schematic diffractograms are shown in green. c, In the out-of-equilibrium scenario of the present work, hexatic order emerges as a result of the optical excitation of a three-dimensional (3D) solid, inducing a dimensional crossover and a spontaneous rotational break-up of the structure (red lines and arrows).
