Channel-closing effects of electronic excitation in solids

Bidirectional residual current in monolayer graphene under few-cycle laser irradiation

By numerically solving the time-dependent Schrödinger equation and semiconductor Bloch equations, the light-induced residual current in monolayer graphene driven by a circularly polarized few-cycle laser is investigated. An evident current direction reversal is disclosed when the amplitude of the driving electric field exceeds a certain threshold value, which is absent in recent investigation [Nature550, 224 (2017)10.1038/nature23900]. Here the internal physical mechanism for the current reversal is inter-optical-cycle interference under a suitable long laser wavelength. Moreover, the reversal-related laser field amplitude depends sensitively on the ratio of ponderomotive energy to photon energy.

Enhancement of the photocurrents injected in gapped graphene by the orthogonally polarized two-color laser field

We theoretically investigate the photocurrents injected in gapped graphene by the orthogonally polarized two-color laser field. Depending on the relative phase, the photocurrents can be coherently controlled by deforming the electron trajectory in the reciprocal space. Under the same field strength, the peak photocurrent in the orthogonally polarized two-color field is about 20 times larger than that for linearly polarized light, and about 3.6 times for elliptically polarized light. The enhancement of the photocurrent can be attributed to an obvious asymmetric distribution of the real population in the reciprocal space, which is sensitive to the waveform of the laser field and related to the quantum interference between the electron trajectories. Our work provides a noncontact method to effectively enhance the injected current in graphene.

Low-energy photoelectron interference structure in attosecond streaking

By numerically solving the time-dependent Schrödinger equation, we theoretically investigate the dynamics of the low-energy photoelectrons ionized by a single attosecond pulse in the presence of an infrared laser field. The obtained photoelectron momentum distributions exhibit complicated interference structures. With the semiclassical model, the originations for the different types of the interference structures are unambiguously identified. Moreover, by changing the time delay between the attosecond pulse and the infrared laser field, these interferences could be selectively enhanced or suppressed. This enables us to extract information about the ionization dynamics encoded in the interference structures. As an example, we show that the phase of the electron wave-packets ionized by the linearly and circularly polarized attosecond pulses can be extracted from the interference structures of the direct and the near-forward rescattering electrons.