  We use an ab-initio approach to design and study a novel two-dimensional
material - a planar array of carbon nanotubes separated by an optimal distance
defined by the van der Waals interaction. We show that the energy spectrum for
an array of quasi-metallic nanotubes is described by a strongly anisotropic
hyperbolic dispersion and formulate a model low-energy Hamiltonian for its
semi-analytical treatment. Periodic-potential-induced lifting of the valley
degeneracy for an array of zigzag narrow-gap nanotubes leads to the band gap
collapse. In contrast, the band gap is opened in an array of gapless armchair
tubes. These unusual spectra, marked by pronounced van Hove singularities in
the low-energy density of states, open the opportunity for interesting physical
effects and prospective optoelectronic applications.
