Probing precise interatomic potentials by nonadiabatic nonlinear phonons

Abstract

Accurately probing the interatomic potential (IP) in crystals is essential for understanding the dynamic mechanisms in phase transitions and chemical reactions. Here, by interrogating laser-induced coherent phonon dynamics, we propose a new kind of optical microscopy for determining effective interatomic potentials beyond the harmonic and adiabatic approximation. This technique is tested against available experimental and first-principles data, by which the interatomic potential of graphene and a few other materials are successfully reconstructed in a large configuration space and beyond the ground state. A significant nonadiabatic effect emerges in nonlinear phonon dynamics and the IP reconstruction, which corrects the anharmonic part of IP much stronger (up to 50%) than the harmonic part. The nonadiabaticity-modulated potentials can lead to ∼10% correction on thermal expansion coefficients and ∼0.3 eV on phase transition barriers. This work offers a new strategy for probing complex interactions in quantum materials and exemplifies the universality of nonadiabaticity, which deserves a full consideration for precisely determining physical properties of quantum many-body systems.