Interaction of carrier envelope phase-stable laser pulses with graphene: the transition from the weak-field to the strong-field regime

Abstract

Ultrafast control of electron dynamics in solid state systems has recently found particular attention. By increasing the electric field strength of laser pulses, the light-matter interaction in solids might turn from a perturbative into a novel non-perturbative regime, where interband transitions from the valence to the conduction band become strongly affected by intraband motion. We have demonstrated experimentally and numerically that this combined dynamics can be controlled in graphene with the electric field waveform of phase-stabilized few-cycle laser pulses (Higuchi et al 2017 Nature 550 224-8; Heide et al 2018 Phys. Rev. Lett. 121 207401). Here we show new experimental data and matching simulation results at comparably low optical fields, which allows us to focus on the highly interesting transition regime where the light-matter interaction turns from perturbative to non-perturbative. We find a 5th order power-law scaling of the laser induced waveform-dependent current at low optical fields, which breaks down for higher optical fields, indicating the transition.

Sub-cycle temporal evolution of light-induced electron dynamics in hexagonal 2D materials

“…Strikingly, the direction of this ballistic current reverses at around 2 V nm −1 . We have shown in [3,17] that the current reversal can be measured and that it is determined by the accumulated phase during subsequent LZ transitions. Note that flipping the phase by π to Φ CEP = π/2 mirrors the vector potential and thus the current direction [3,18].…”

“…This time regime is in particular important to study fundamental processes such as electronic decoherence, resulting from dephasing and electron-electron scattering on the femtosecond timescale. Alternatively to trARPES, indirect measurements, such as the generation of high-harmonics [40,42,[52][53][54][55] or a residual conducing current [3,16,17,56] can reveal information about the electron dynamics. Whereas the first one is sensitive to the inter-and intraband electron dynamics during the laser pulse, the latter is sensitive to the residual current density, which is a result of coherent quantum path interference of different Bloch trajectories [3,23].…”

Light-field and spin-orbit-driven currents in van der Waals materials

“…They demonstrated that the sign of the current reverses at an optical peak field of about 2 Vnm −1 . This reversal was interpreted as a transition to the strongfield regime where the electron dynamics are dominated by Landau-Zener-Stückelberg interference of trajectories in reciprocal space [80,81]. It is worth noting that, because of graphene's peculiar band structure, the response is highly nonlinear [86,198] and the required field strength to achieve light-field-driven dynamics is about one order of magnitude smaller than that for solid-state dielectrics [82,199].…”

“…Recent reports on graphene suggest that even attosecond dynamics can be explored in two-dimensional van der Waals materials with carrier-envelope phase stabilized lasers in the strong-field regime [80,81]. This strongfield regime is achieved for decent peak electric fields of about 2 Vnm −1 for a near-infrared few-cycle laser [81], which suggests the occurrence of light-field-driven currents, as reported mainly for bulk solids so far [82,[83][84][85], also in TMDs and further atomistic van der Waals materials. Nowadays, electron dynamics which are directly driven via the amplitude and phase of optical fields represent the fastest experimentally accessible time scale (Figure 1).…”

Plunging in the Dirac sea using graphene quantum dots

“…Many theoretical and experimental investigations have focused on the interaction of graphene with a (homogeneous) laser field [24][25][26][27][28]. The regime of strong fields, whereby multiphotonic effects, the holy grail of atomic physics, start to be important and may lead to new physical phenomena, have also been investigated [14][15][16][17][18][29][30][31][32]. For inhomogeneous fields, some work has also been performed.…”