Solids in ultrafast strong laser fields: topological nanophotonic phenomena (Conference Presentation)

Abstract

A strong optical field, ~0.1-1 V/A, changes solids on the attosecond time scale, i.e., within an optical cycle. Such fields drive ampere-scale currents in dielectrics and adiabatically controls their properties, including optical absorption and reflection, extreme UV absorption, and generation of high harmonics in a non-perturbative manner [1-5]. We will concentrate on ultrafast phenomena defined by nontrivial topological properties of solids in the reciprocal space, which are described by non-zero Berry (topological) curvature and Berry flux, which to a significant degree define their behavior in strong optical fields. In particular, these are graphene [6, 7], silicene [8], and surfaces of topological insulators (TI’s) (semimetals) [9], monolayer transitional metal dichalcogenides (TMDC’s) [10], black phosphorus and phosphorene (direct bandgap semiconductors), and hexagonal boron nitride (h-BN) (dielectric). For two-dimensional semiconductors such a TMDC’s, we predict a new attosecond phenomenon in a strong chiral optical fields – a topological resonance [11]. This manifests itself in the establishment of a strong valley polarization during just a single optical cycle, i.e., in the fundamentally fastest way possible. It structures the reciprocal space into topologically distinct areas. This phenomenon is promising for ultrafast recording of both classical bits and cubits for quantum information processing. Another distinct class of two-dimensional systems in a strong pulse field that we consider are surfaces of TI’s. These are crystals characterized a non-zero topological invariant Z2=1 where bulk is semiconducting but surfaces are Dirac semimetals. In the surface reciprocal space, they contain a single Dirac point with a Berry phase of ±π at the Г-point. Subjected to circularly-polarized ultrashort strong pulses they exhibit chiral textures in the reciprocal space and topologically-protected currents [9]. Finally, we will present our latest results on Weyl semimetals in ultrafast strong chiral fields. Such fields induce topological resonances and ultrafast bulk currents on femtosecond time scales.