Optical current generation in graphene: CEP control vs. ω + 2ω control

The injection of directional currents in solids with strong optical fields has attracted tremendous attention as a route to realize ultrafast electronics based on the quantum-mechanical nature of electrons at femto-to attosecond timescales. Such currents are usually the result of an asymmetric population distribution imprinted by the temporal symmetry of the driving field. Here we compare two experimental schemes that allow control over the amplitude and direction of light-field-driven currents excited in graphene. Both schemes rely on shaping the incident laser field with one parameter only: either the carrier-envelope phase (CEP) of a single laser pulse or the relative phase between pulses oscillating at angular frequencies co and 2 omega, both for comparable laser parameters. We observe that the efficiency in generating a current via two-color-control exceeds that of CEP control by more than two orders of magnitude (7 nA vs. 18 pA), as the omega + 2 omega field exhibits significantly more asymmetry in its temporal shape. We support this finding with numerical simulations that clearly show that two-color current control in graphene is superior, even down to single-cycle pulse durations. We expect our results to be relevant to experimentally access fundamental properties of any solid at ultrafast timescales, as well as for the emerging field of petahertz electronics.

Automated summary

By comparing two experimental schemes for controlling light-field-driven currents in graphene, it was found that two-color control is more efficient than CEP control by over two orders of magnitude. The omega + 2 omega field exhibits significantly more asymmetry in its temporal shape, leading to the superior efficiency of two-color current control. This finding is supported by numerical simulations, suggesting the relevance of these results for fundamental properties of solids at ultrafast timescales and the field of petahertz electronics.