Discrete breathers in 2D and 3D crystals

Abstract

Discrete breathers (DB) are spatially localized, large‐amplitude vibrational modes in defect‐free nonlinear lattices. Recent numerical and experimental studies have confirmed that DB exist in crystals. In the present work, we briefly describe the well‐known existence conditions of DB in crystals and present our recent results on DB in 2D crystals such as graphene and graphane and in 3D crystals such as alkali halide crystals and pure metals. The possible role of DB in solid state physics and materials science is discussed. Stroboscopic picture of atomic motions in the vicinity of discrete breather excited in graphene homogeneously strained with ϵxx=0.3, ϵyy=−0.1. Displacements of atoms from the equilibrium lattice positions are multiplied by the factor 4 for clarity. The discrete breather is of high spatial localization, so that only two atoms oscillate with a large amplitude.

Crossover from ballistic to normal heat transport in theϕ4lattice: If nonconservation of momentum is the reason, what is the mechanism?

“…For the hard-type nonlinearity considered (β > 0), only DBs with frequencies lying in the range denoted by 2 in Fig. 1, i.e., above the linear phonon band, are possible [20][21][22][23]. It can also be expected that, the nonlinearity together with the phonon dispersion as shown in Fig.…”

“…However, obviously such a theoretical model does not involve the effects of other nonlinear excitations, such as solitons [19] and discrete breathers (DBs) [20][21][22][23].…”

Возбуждение Щелевых Дискретных Бризеров В Кристалле Состава a-=sub=-3-=/Sub=-B Потоком Частиц

“…Молекулярно-динамические расчеты подтверждают возможность воз-буждения ДБ в чистых металлах [24][25][26][27][28][29][30] и в упорядо-ченных сплавах [31][32][33][34][35][36][37][38][39][40]. Появились первые работы по изучению свойств ДБ в низкоразмерных кристаллах, ос-нованные на первопринципных расчетах, учитывающих электронную структуру вещества [41][42][43].…”

Quantum tunneling in gap discrete breathers

“…DBs are spatially localized large-amplitude vibrational modes in lattices that exhibit strong anharmonicity [14][15][16][17][18][19][20][21][22][23]. Due to the crystal anharmonicity, the frequency of atomic oscillations increase or decrease with increasing amplitude so that the DB frequency lies outside the phonon frequency band, which explains the weak DB coupling with phonons and, consequently, their robustness at elevated temperatures.…”

“…In the former case, all atoms vibrate with the same frequancy, while in the latter case, they vibrate with different but commensurate frequencies. DBs can be excited either thermally or by external driving, as was observed experimentally [17,18] and modelled in various physical systems [19][20][21][22][23][24][25][26].…”