A new study published in Physical Review Letters demonstrates how intense terahertz light can parametrically control atomic vibrations, providing a new blueprint for ultrafast material engineering.
Researchers from CNR-SPIN, including Francesco Gabriele, Filomena Forte, and Mario Cuoco, in collaboration with an international team of research partners worldwide, have discovered a novel way to manipulate the structural properties of materials at the atomic scale. By utilizing intense terahertz pulses, the team successfully achieved the parametric excitation of Raman-active phonons in Lanthanum Aluminate (LaAlO3), a commonly used substrate in oxide electronics.
A central pillar of this discovery was the theoretical framework provided by the group at CNR-SPIN (Salerno). In many functional materials, atoms are arranged in a centrosymmetric pattern, meaning they do not respond easily to direct electrical stimulation. The key finding of the study is that, in centrosymmetric materials, an intense terahertz laser can generate pairs of acoustic phonons and that the interaction between the Raman-active phonon and these acoustic modes leads to a parametric driving of the Raman-active mode itself. This framework successfully identified subharmonic fingerprints of the phonon dynamics, as unique signatures of a parametric driving mechanism, a phenomenon analogous to a classical pendulum with a time-dependent frequency.
This discovery paves the way for novel strategies to control lattice vibrations in centrosymmetric materials and to manipulate them on ultrafast timescales, thereby providing an alternative route to tuning structural phases and their associated macroscopic properties. The implications of these findings are generally vast and carry broad significance for the ultrafast, condensed-matter, and materials-science communities, and are expected to stimulate further exploration of THz-driven strategies for controlling phonon-based functionalities.
As LaAlO3 is a fundamental building block for oxide heterostructures, the uncovered mechanism could soon be used to control quantum states at functional interfaces in a nonlocal fashion.
Full reference: Terahertz-Driven Parametric Excitation of Raman-Active Phonons in LaAlO3, M. Basini, V. Unikandanunni, F. Gabriele, M. Cross, A.M. Derrico, A.X. Gray, M. C. Hoffmann, F: Forte, M. Cuoco, S. Bonetti, Physical Review Letters 136, 156902 (2026); DOI: https://doi.org/10.1103/57p8-7mh9
