Mind the (van der Waals) Gap

An intense beam of light can reshape the distribution of electrons in a two-dimensional material at sub-50 femtoseconds timescale, revealing a transient regime of electronic dynamics before substantial atomic motion develops.

Controlling materials with light requires understanding how their electrons respond to intense, ultrashort laser pulses. At interfaces between atomically thin materials, this response can be particularly complex: electrons can move between layers, changing the local electrical polarization on the timescales that are difficult to access experimentally.

Using real-time first-principles simulations, Dr. Muhammad Sufyan Ramzan and Prof. Caterina Cocchi together with Prof. Giancarlo Soavi investigated a MoS2/WSe2 heterobilayer subject to pulses of increasing intensity for about 100 fs. The results show that intense laser fields drive a nonlinear redistribution of electronic charge, producing a pronounced transient interfacial polarization. At the highest intensities, electrons spread beyond the individual layers, while changes in the emitted high-harmonic spectrum reveal the transition to a strongly nonlinear optical response.

These findings, published on Nano LettersExternal link, reveal how intense light can reshape the electronic properties of a two-dimensional interface before substantial lattice motion develops. The results provide a foundation for understanding ultrafast polarization dynamics and exploring new ways to control the response of atomically thin materials with light.