Band-gap generation and excitation of conduction electrons in graphene by THz laser fields

Faisal F. Band-gap generation and excitation of conduction electrons in graphene by THz laser fields. MOLECULAR PHYSICS. 2017;115(15-16):1768-1774.Graphene is a one-atom-thin 2D layer of hexagonal rings of carbon atoms (or, a giant 2D 'carbonmolecule') whose low-energy quasi-particles are charged and massless Dirac fermions which follow the relativistic Dirac equation in 2D. Using a recently developed theory of interaction of graphene with intense laser fields, we briefly discuss two phenomena of interest: (1) the lifting of degeneracy of graphene at the K-points by THz laser interaction and (2) induction of anisotropic electron distributions in the conduction band from the occupied valence band by absorption of one-, two-, or multiple THz photons. The first process is analogous to a phase transition of a pristine graphene from a semi-metal into a semiconductor within a time scale determined by the ultrashort pulse duration of the laser. The second process may permit control of electron currents in graphene whose magnitude and direction may be controlled simultaneously by controlling the THz laser parameters (e.g. pulse duration, field strength or polarisation). [GRAPHICS]