We discuss the topological properties of graphene superlattices excited by ultrafast circularly-polarized laser pulses with strong electric field amplitude, aiming to directly observe of the Berry phase, a geometric quantum phase encoded in the graphene’s electronic wave function. As a continuing research on our recent paper, Phys. Rev. B 96, 075409, we aim to show that the broken symmetry system of graphene superlattice and the Bragg reflection of electrons creates diffraction and “which way” interference in the reciprocal space reducing the geometrical phase shift and making it directly observable in the electron interferograms. Such a topological phase shift acquired by a carrier moving along a closed path of crystallographic wave vector is predictably observable via time and angle resolved photoemission spectroscopy (tr-ARPES). We believe that our result is an essential step in control and observation of ultrafast electron dynamics in topological solids and may open up a route to all-optical switching, ultrafast memories, and petahertz-scale information processing technologies.
We propose an attosecond strong optical field interferometry in graphene which reveals the chirality of graphene without employing a magnetic field. A circularly polarized optical pulse with strong amplitude and femtosecond time scale causes the electron to circle in the reciprocal space through which it accumulates the dynamic phase along the closed trajectory as well as the nontrivial geometric phase known as Berry’s phase. The resulting interference fringes carry rich information about the electronic spectra and interband dynamics in graphene near the Dirac points. Our findings hold promises for the attosecond control and measurement of electron dynamics in condensed matters as well as understanding the topological nature of the two-dimensional Dirac materials.
This paper investigates the interaction of buckled Dirac materials (silicene and germanene) with ultrashort and ultrastrong optical pulses. Highly intensive few-cycle pulses strongly modify the electronic and optical properties of these two dimensional materials. Electron dynamics in such a short optical pulse is coherent and can be robustly controlled by altering the propagation direction, as well as the polarization angle of the pulse. The strong nonlinearity of the system for fields applied (~ V/Å) causes the violation of the charge (C) and parity (P) symmetries, effectively reducing the system’s symmetry from hexagonal to triangular. Such symmetry violations are related to the electron transfer between the sublattices caused by the normal field component and result in nonreciprocity, optical rectification and the appearance of a cross current.