Fig. 1 (IMAGE)
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Circularly polarized laser pulse (a-c) versus a hencomb laser pulse (d-f). The vector potential of a circularly polarized lightwave applied to the two dimensional material Tungsten Diselenide generates no residual current after the laser pulse (a,b), solely exciting a valley charge state, (c), in which the Bloch velocities of all excited states cancel by virtue of the charge excitation being positioned at the valley centre (the apex of the Brillouin zone indicated by the red lines). In contrast a hencomb pulse, in which the circularly polarized lightwave is augmented by a symmetry breaking linearly polarized THz component generates a pronounced residual current (d,e), which results as the symmetry breaking shifts the excited charge off the valley centre (f), leading to non-cancellation of current over the excited charge distribution. While the THz pulse by itself leads to no excitation, in combination with circularly polarized light the THz polarization vector and amplitude are the key parameters that fully control the final current state.
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