Evidence of Opto-Mechanical-Driven Topological Phase Transition in SnSe

Important advances have been recently made in the search for materials with complex multi-phase landscapes that host photoinduced metastable collective states with exotic functionalities, such as high-temperature superconductivity or topological switches. In almost all cases so far, the desired phases are accessed by exploiting light-matter interactions via the imaginary part of the dielectric function, through above-bandgap or resonant mode excitation. Recently, inspired by optical tweezers, a novel non-resonant optomechanical driving force was theoretically proposed to drive topological phase switching in tin selenide (SnSe) by using off-resonant light excitation, mediated by the real part of the dielectric function. The absence of direct absorption via the imaginary part signifies the potential of this approach over traditional methods in selectively driving transitions with reduced energy consumption and ultrafast switch speed. Here we study mid-infrared-excited SnSe with time-domain Raman scattering and a suite of advanced spectroscopies sensitive to the dynamic structure and symmetry of the light-induced phase. The abrupt suppression of A_g Raman modes above a critical MIR field strength without discernible softening is consistent with a structural distortion towards a higher symmetry phase with dramatically modified optical properties via a non-thermal driving mechanism. The high reflectivity contrast emphasizes the potential of harnessing these phase control handles for telecommunication applications. Further corroborated with transient reflectivity measurements and state-of-the-art first-principles calculations, our study provides evidence for an opto-mechanical-driven topological phase transition, defining novel opportunities for inducing hidden quantum phases with unique functional properties.