Fig. 1: Atomic motion and atomic displacement associated with resonant driving of the TO (E_1u) phonon mode.

a Honeycomb lattice arrangement of hexagonal boron nitride. Arrows illustrate the motion of atoms under resonant optical excitation. The two species move oppositely from each other in plane and across all layers for the IR-active TO (E_1u) mode. b Simulated atomic displacements, in units of Bohr radii a₀, of boron and nitrogen ions in TO (E_1u)-excited hBN. A 25-fs FWHM, 1 × 10¹² W/cm² pulse excites the lattice dynamics. The TDDFT simulations do not include any damping terms through which to estimate the relaxation time. c Peak amplitude of atomic displacements as a function of pump intensity, fit to I^1/2 with a small linear-in-intensity correction. Displacements nearing 10% of the equilibrium lattice constant are achievable before the onset of damage.