Re-emergent direct–indirect band gap transitions in carbon nanotubes under shear strains

Electronic structures of single-walled carbon nanotubes under varying shear strains are studied with the use of pseudopotential density functional method. We present a new scheme to induce shear strains in one-dimensional materials like nanotubes without introducing artificial edge atoms. It is found that the band gap of semiconducting zigzag nanotubes exhibits reemerging direct–indirect transitions as they are twisted. The breaking of the three-fold rotational symmetry and the electron–hole symmetry of corresponding graphitic band structures under shear is shown to be the origin of the behavior in the band gap.