Charge carrier anisotropic motion in twisted few-layer graphene

In twisted bilayer the graphene layers are equivalent. However, even in this simplest graphene stack, phenomena like counterflow conductivity of separately contacted layers, neutrino-like oscillations and collimated electron transport are predicted to result from rotational symmetry breaking. These exotic properties are closely related to chiral spinor-like wave function of the quasiparticles in graphene. Moreover, as a distinctive feature of the chirality, the propagation of Dirac fermions under external periodic potential is expected to be anisotropic, manifesting anisotropic group velocities, anisotropic gaps in electronic structure at minizone boundary (MB) and the formation of superlattice Dirac points.

 We grow few layer graphene with various number of layers and twist configurations.The dependence of the interlayer coupling on the twist angle is analyzed and, in the domains with tri-layers and more, if different rotations are present, the electrons in weaker coupled adjacent layers are shown to have different properties manifested by coexisting van Hove singularities, moiré superlattices with corresponding superlattice Dirac points, and charge carrier group velocity renormalizations. Moreover, pronounced anisotropy in the charge carrier motion, opening a possibility to transform strongly coupled graphene bilayers into quasi one-dimensional conductors, is observed.