Photoinduced Non-thermal Topological Phase Transition in Bi₂Se₃ Driven by Coherent Interlayer Vibrations

We present the non-thermal route of photoinduced topological phase transition driven by interlayer vibrations. By combining ultrafast optical and THz spectroscopy, which are sensitive to interlayer vibrations through photoelastic effects and Dirac surface state leading to low-energy conductivity in topological insulator Bi2Se3, we found that interfacial modes, which correspond to uniaxial strains and modulate interlayer spacing, involve the photoinduced topological phase switching from topological insulator toward normal insulator. Our observations provide fundamental insight to nanomechanical lattice-topological phase interactions for possible optoelectronic and photonic applications based on optically-driven phase transition switching at ultrafast timescales.