Effect of discrete breathers on macroscopic properties of the Fermi-Pasta-Ulam chain

The effect of discrete breathers (DBs) on macroscopic properties of the Fermi-Pasta-Ulam chain with symmetric and asymmetric potentials is investigated. The total to kinetic energy ratio (related to specific heat), stress (related to thermal expansion), and Young's modulus are monitored during the development of modulational instability of the zone boundary mode. The instability results in the formation of chaotic DBs followed by the transition to thermal equilibrium when DBs disappear due to energy radiation in the form of small-amplitude phonons. It is found that DBs reduce the specific heat for all the considered chain parameters. They increase the thermal expansion when the potential is asymmetric and, as expected, thermal expansion is not observed in the case of symmetric potential. The Young's modulus in the presence of DBs is smaller than in thermal equilibrium for the symmetric potential and for the potential with a small asymmetry, but it is larger than in thermal equilibrium for the potential with greater asymmetry. Our results can be useful for setting experiments on the identification of DBs in crystals by measuring their macroscopic properties.Comment: 9 pages, 10 figures; v3: some changes in the text, references added; matches the published versio

Effect of damping on kink ratchets in the Klein-Gordon lattice free of the Peierls-Nabarro potential

Ratchet of kink under harmonic ac driving force in the discrete Klein-Gordon model with asymmetric potential and with a damping term is investigated numerically. A particular feature of the considered discrete model is that supported kinks are free of the Peierls-Nabarro potential (PNp). It is demonstrated that, depending on the strength of damping, the drift velocity of the kink can be positive (weak damping) or negative (strong damping). The absence of PNp results in a weak dependence of kink drift velocity on the discreteness parameter

Effect of damping on kink ratchets in the Klein-Gordon lattice free of the Peierls-Nabarro potential

Ratchet of kink under harmonic ac driving force in the discrete Klein–Gordon model with asymmetric potential and with a damping term is investigated numerically. A particular feature of the considered discrete model is that supported kinks are free of the Peierls–Nabarro potential (PNp). It is demonstrated that, depending on the strength of damping, the drift velocity of the kink can be positive (weak damping) or negative (strong damping). The absence of PNp results in a weak dependence of kink drift velocity on the discreteness parameter.This work was supported by the RFBR-DST Indo-Russian grant 08-02-91316-Ind-a and the RFBR grant 09-08-00696-

Supersonic Motion of Atoms in an Octahedral Channel of fcc Copper

In this work, the mass transfer along an octahedral channel in an fcc copper single crystal is studied for the first time using the method of molecular dynamics. It is found that the initial position of the bombarding atom, outside or inside the crystal, does not noticeably affect the dynamics of its motion. The higher the initial velocity of the bombarding atom, the deeper its penetration into the material. It is found out how the place of entry of the bombarding atom into the channel affects its further dynamics. The greatest penetration depth and the smallest dissipation of kinetic energy occurs when the atom moves exactly in the center of the octahedral channel. The deviation of the bombarding atom from the center of the channel leads to the appearance of other velocity components perpendicular to the initial velocity vector and to an increase in its energy dissipation. Nevertheless, the motion of an atom along the channel is observed even when the entry point deviates from the center of the channel by up to 0.5 Å. The dissipated kinetic energy spent on the excitation of the atoms forming the octahedral channel is nearly proportional to the deviation from the center of the channel. At sufficiently high initial velocities of the bombarding atom, supersonic crowdions are formed, moving along the close-packed direction ⟨1¯10⟩, which is perpendicular to the direction of the channel. The results obtained are useful for understanding the mechanism of mass transfer during ion implantation and similar experimental techniques