Ultrafast Ferroelectric Ordering on the Surface of a Topological Semimetal MoTe2

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Abstract
Transient tuning of material properties by light usually requires intense laser fields in the nonlinear excitation regime. Here, we report ultrafast ferroelectric ordering on the surface of a paraelectric topological semimetal 1T’-MoTe2 in the linear excitation regime, with the order parameter directly proportional to the excitation intensity. The ferroelectric ordering, driven by a transient electric field created by electrons trapped ångstroms away from the surface in the image potential state (IPS), is evidenced in two-photon photoemission spectroscopy showing the energy relaxation rate proportional to IPS electron density, but with negligible change in the free-electron-like parallel dispersion. First-principles calculations reveal an improper ferroelectric ordering associated with an anharmonic interlayer shearing mode. Our findings demonstrate an ultrafast charge-based pathway for creating transient polarization orders.
Funding Information
  • Office of Energy Efficiency and Renewable Energy
  • Office of Naval Research (N00014-18-1-2080)
  • Office of Science (DE-SC0010692)

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