Intrinsic 1 phase induced in atomically thin 2H-MoTe₂ by a single terahertz pulse

The polymorphic transition from 2H to 1$$-MoTe₂, which was thought to be induced by high-energy photon irradiation among many other means, has been intensely studied for its technological relevance in nanoscale transistors due to the remarkable improvement in electrical performance. However, it remains controversial whether a crystalline 1$$ phase is produced because optical signatures of this putative transition are found to be associated with the formation of tellurium clusters instead. Here we demonstrate the creation of an intrinsic 1$$ lattice after irradiating a mono- or few-layer 2H-MoTe₂ with a single field-enhanced terahertz pulse. Unlike optical pulses, the low terahertz photon energy limits possible structural damages. We further develop a single-shot terahertz-pump-second-harmonic-probe technique and reveal a transition out of the 2H-phase within 10 ns after photoexcitation. Our results not only provide important insights to resolve the long-standing debate over the light-induced polymorphic transition in MoTe₂ but also highlight the unique capability of strong-field terahertz pulses in manipulating quantum materials.