Effect of strain on gap discrete breathers at the edge of armchair graphene nanoribbons

Linear and nonlinear vibration modes of strained armchair graphene nanoribbons with free edges are investigated by means of atomistic modeling. It is shown that phonon modes can be divided into two groups, the XY-modes with the displacements of atoms in the nanoribbon plane, and the Z-modes with atomic displacements normal to the nanoribbon plane. Strained nanoribbons possess a sufficiently wide gap in the phonon spectrum of the XY-modes so that a gap discrete breather (DB) can be excited. Large-amplitude DBs exist within the strain range 0.125 < epsilon(xx) < 0.20. At larger strains an attempt to excite a DB results in breaking of the nanoribbon, while at smaller strains the gap in the phonon spectrum of the XY-modes is either too narrow or absent. DBs can have energy up to 1 eV and the maximal DB energy is larger for smaller strain of the nanoribbon. A possible role of DBs in the fracture of strained graphene nanoribbons at finite temperatures is discussed. Copyright (c) EPLA, 2013