LAUSR

Tungsten ditelluride is a layered transition-metal dichalcogenide that crystalizes in a distorted hexagonal net with an orthorhombic unit cell. The lack of inversion symmetry in this phase leads to a predicted new topological semimetal with unique optoelectronic properties. Here, we use intense single cycle THz pulses to trigger a structural deformation in WTe2 and probe its dynamics using femtosecond resolution electron diffraction techniques. We observe large amplitude interlayer shear oscillations at 0.25 THz that occur along the in-plane transition state separating the orthorhombic and monoclinic phases of the material, identified by measuring structure factor modulations of many Bragg reflections. The response scales linearly with the applied THz field but the initial atomic displacements occur always in the direction towards that of the monoclinic phase, independent of whether the THz field is applied parallel or antiparallel to this crystallographic direction. We also report on recent results using mid-infrared excitation which show similar structural deformations but of even larger amplitude. This work opens up new possibilities for ultrafast THz field control over the topological properties of solids.