Opto-Mechanical Structural Transitions in SnSe Driven by Mid-Infrared Light Pulses

A central goal in materials research is to develop means for controlling and inducing new phases of matter with unique functionalities. With respect to using light to control matter, previous work has mostly focused on above-bandgap or resonant mode excitation, accessing the imaginary part of the dielectric function. Here we present new experimental results using a suite of advanced spectroscopies to show evidence for a novel optomechanical driving force in the chalcogenide material tin selenide (SnSe) using mid-infrared, below-gap femtosecond optical pulses. Femtosecond time-resolved Raman scattering shows an abrupt suppression of Raman modes above a threshold fluence consistent with a distortion towards the high-symmetry rocksalt phase of SnSe. This is further corroborated by transient reflectivity measurements, time-resolved x-ray scattering, and first principles calculations, thereby defining new possibilities for manipulating the structure and functionality of SnSe and related chalcogenide materials.