Mode-selective control over the structural phase transition in atomic indium wires on silicon*

Driving a phase transition along a nonequilibrium pathway via optical control of coherent phonons has proven powerful in controlling electronic and structural phases on ultrafast time scales [1]. In this regard, charge density wave systems have emerged as natural targets as their amplitude modes are directly linked with the associated structural phase transition. Coherent manipulation of these modes thus allows to guide the system from one state to another and provides access to the complex geometry of the underlying potential energy landscape. Here, using ultrafast low-energy electron diffraction and tailored pulse sequences, we demonstrate mode-selective control over the phase transition of In/Si(111) [2,3]. We track key vibrational modes along transient trajectories and reveal characteristics of the underlying potential landscape, corroborated by DFT calculations. The manipulation of vibrational coherences provides a playground for exploring nonequilibrium dynamics in strongly correlated systems and promises the active selection of their properties.

[1] Nova, T. F et al., Science 364, 1075–1079 (2019); [2] Horstmann, J. G. et al., Nature 583, 232-236 (2020); [3] Böckmann, H. et al., arXiv:2108.13966