**Supersonic voidions in 2D Morse lattice**

IA Shepelev and SV Dmitriev and AA Kudreyko and MG Velarde and EA Korznikova, CHAOS SOLITONS & FRACTALS, 140, 110217 (2020).

DOI: 10.1016/j.chaos.2020.110217

Dynamics of M x 1-crowdion clusters (M = 1, 2 or 3) and vacancy clusters is analyzed in 2D triangular lattice with Morse interactions. Topological defects are created in the lattice by kicking three neighboring atoms in the three neighboring close-packed atomic rows along the rows. Initial velocity of the atoms in the inner row, v(inn), can be positive or negative, while the velocities of both atoms in the outer rows, v(out), are equal and positive. The case of v(inn) = v(out) was analysed earlier and it was found that if the initial velocity is sufficiently large then a 3 x 1-crowdion cluster and a three-vacancy are formed. Two major effects are reported in the case of v(inn) not equal v(out) analyzed here. (i) Due to the difference in the initial velocities, topological defects can be produced in the lattice with smaller initial energy than in the case of v(inn) = v(out). (ii) In certain range of the initial velocities, a vacancy can appear at a distance of dozens interatomic distances from the initiation point, moving along the close-packed row with supersonic speed. Such moving vacancy is called voidion and mechanism of its formation and motion is revealed. Our results uncover new mechanisms of mass transfer by solitary waves in nonlinear lattices. (C) 2020 Elsevier Ltd. All rights reserved.

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