Intrinsic localized modes observed in the high-temperature vibrational spectrum of NaI

Manley, M. E.; Sievers, A. J.; Lynn, J. W.; Kiselev, S. A.; Agladze, N. I.; Chen, Ying; Llobet, Anna; Alataş, Ahmet

doi:10.1103/physrevb.79.134304

Cited by 126 publications

(145 citation statements)

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“…While ILMs are spatially localized nonlinear excitations that occur in perfect crystals [28][29][30] , in this model a local enhancement of the nonlinearity associated with off-centring Pb atoms 31 instigates the formation of ILMs on cooling [25][26][27] . The ILM frequency then slows below that of the TO phonon into the frequency gap between the TA and TO phonons, and eventually vanishes as PNRs become static [25][26][27] .…”

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confidence: 99%

Phonon localization drives polar nanoregions in a relaxor ferroelectric

et al. 2014

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Relaxor ferroelectrics exemplify a class of functional materials where interplay between disorder and phase instability results in inhomogeneous nanoregions. Although known for about 30 years, there is no definitive explanation for polar nanoregions (PNRs). Here we show that ferroelectric phonon localization drives PNRs in relaxor ferroelectric PMN-30%PT using neutron scattering. At the frequency of a preexisting resonance mode, nanoregions of standing ferroelectric phonons develop with a coherence length equal to one wavelength and the PNR size. Anderson localization of ferroelectric phonons by resonance modes explains our observations and, with nonlinear slowing, the PNRs and relaxor properties. Phonon localization at additional resonances near the zone edges explains competing antiferroelectric distortions known to occur at the zone edges. Our results indicate the size and shape of PNRs that are not dictated by complex structural details, as commonly assumed, but by phonon resonance wave vectors. This discovery could guide the design of next generation relaxor ferroelectrics.

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confidence: 99%

Phonon localization drives polar nanoregions in a relaxor ferroelectric

et al. 2014

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“…Первая успешная попытка в моделиро-вании ДБ была осуществлена для щелочно-галоидного кристалла NaI с ионным межатомным взаимодействием [7]. Для этого же кристалла, была проведена серия экс-периментов по обнаружению ДБ при высоких темпера-турах в тепловом равновесии [22].…”

Section: о типе нелинейности класси-ческих парных потенциаловunclassified

The reason for existence of discrete breathers in 2D and 3D Morse crystals

Korznikova¹,

Kistanov²,

Sergeev³

et al. 2016

LoM

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It is known that crystals can support discrete breathers (DBs) -periodic in time and spatially localized vibrational modes. DB does not radiate energy, as its frequency does not lie within the spectrum of small-amplitude traveling waves (phonons). DB frequency can leave the spectrum of low-amplitude oscillations due to the nonlinearity of the interatomic potentials, as it is well known that the frequency of a nonlinear oscillator depends on the amplitude. Theoretically, it was shown that DB cannot exist in a one-dimensional chain of identical point masses interacting with each other through the Toda, Born-Mayer, Lennard-Jones or Morse potential. The reason of non-existence of DB is the softness of the considered potentials, which does not allow to form a spatially localized mode with frequency above the phonon spectrum. On the basis of this rigorous result, it was concluded that because of the softness of the interatomic interactions in crystals with a simple structure (e.g., in pure metals) existence of DB is very unlikely. Attention should be paid to crystals with a gap in phonon spectrum. In such crystals localized vibrational modes may have frequencies decreasing with amplitude and entering the gap of the phonon spectrum. The first successful attempt to excite a gap DB in alkali halide NaI crystal dates back to 1997, for this purpose, the method of molecular dynamics was used. However, in 2011 DBs with frequencies higher than the phonon spectrum were discovered in pure metals, which poses the question about the conditions of the existence of DBs in crystals with realistic interatomic potentials. In this paper we show that the dimension of the crystal is important, and the Morse crystals of dimension higher than one can support DBs with frequencies above the phonon spectrum. Известно, что кристаллы могут поддерживать существование дискретных бризеров (ДБ) -периодических во вре-мени пространственно-локализованных колебательных мод. ДБ не излучают энергию, так как их частота не лежит в спектре малоамплитудных бегущих волн (фононов). Выход частоты ДБ из спектра малоамплитудных колебаний происходит за счет нелинейности во взаимодействии атомов, ведь известно, что частота нелинейных осцилляторов зависит от амплитуды колебаний. Теоретически было показано, что ДБ не могут существовать в одномерной це-почке одинаковых точечных масс, взаимодействующих друг с другом посредством потенциалов Тоды, Борн-Маера,

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“…Therefore, discrete breathers have attracted intense interest in many areas of physics as well as chemistry and biology over the past three decades, see, e.g., the most recent review articles [5][6][7]. Intriguingly, discrete breathers have been experimentally observed in a wide variety of different media such as atomic lattices 8,9 , alkali halides 10,11 , graphite 12 , charge-transfer solids 13 , Josephson junction arrays 14,15 , coupled antiferromagnetic layers [16][17][18][19] , layered high-T c superconductors 20 , micromechanical cantilever arrays [21][22][23] , torsionally coupled pendula 24 , granular crystals 25 , electrical lattices [26][27][28][29][30] , optical waveguides and photonic crystals [31][32][33][34][35] , Bose-Einstein condensation 36 , biopolymers 37,38 , and so on.…”

Section: Introductionmentioning

confidence: 99%

“…However, many numerical results [44][45][46][47][48][49] and experimental results 8,10,11,19 indicate that discrete breathers can be observed in thermal equilibrium. Wherein the experiments Refs.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, there is an energy threshold to observe a discrete breather. Many experiments have indeed revealed the existence of the energy threshold 8,[10][11][12]14,[16][17][18][19]31,33 . The size-dependent and dimension-dependent energy thresholds of discrete breathers have been analytically obtained in nonlinear Hamiltonian systems [39][40][41][42][43] .…”

Section: Introductionmentioning

confidence: 99%

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Energy thresholds of discrete breathers in thermal equilibrium and relaxation processes

Ling

et al. 2017

Chaos: An Interdisciplinary Journal of Nonlinear Science

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So far, only the energy thresholds of single discrete breathers in nonlinear Hamiltonian systems have been analytically obtained. In this work, the energy thresholds of discrete breathers in thermal equilibrium and the energy thresholds of long-lived discrete breathers which can remain after a long time relaxation are analytically estimated for nonlinear chains. These energy thresholds are size dependent. The energy thresholds of discrete breathers in thermal equilibrium are same as the previous analytical results for single discrete breathers. The energy thresholds of long-lived discrete breathers in relaxation processes are different from the previous results for single discrete breathers but agree well with the published numerical results known to us. Because real systems are either in thermal equilibrium or in relaxation processes, the obtained results could be important for experimental detection of discrete breathers. a) Electronic mail: meanyee@mail.ustc.edu.cn b) Electronic mail: zjding@ustc.edu.cn 1 Discrete breather is an intrinsic spatially localized nonlinear excitation which can be excited in any kind of discrete nonlinear systems. They can be excited both in thermal equilibrium and in relaxation processes. Once the long-lived discrete breathers are formed in the relaxation processes, the energy relaxations are very slow. The energy thresholds of discrete breathers in thermal equilibrium and relaxation processes can be only numerically estimated so far because of the strong interactions between breathers with other excitations, for instance, phonons. They are thus regarded as identical to the previous analytical energy thresholds of single discrete breathers in Hamiltonian systems. In this work, the energy thresholds of discrete breathers in thermal equilibrium and relaxation processes and thus of the slow energy relaxations are analytically estimated. The energy thresholds of discrete breathers in thermal equilibrium are same as the previous results for single discrete breathers. However, the energy thresholds of long-lived discrete breathers in relaxation processes are different from the previous results. Remarkably, they agree well with the published numerical results known to us. Real systems are either in thermal equilibrium or in relaxation processes. Therefore, the obtained energy thresholds, especially the size-dependence of them, are expected to be important for experimental detection of discrete breathers.

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Intrinsic localized modes observed in the high-temperature vibrational spectrum of NaI

Cited by 126 publications

References 23 publications

Phonon localization drives polar nanoregions in a relaxor ferroelectric

Phonon localization drives polar nanoregions in a relaxor ferroelectric

The reason for existence of discrete breathers in 2D and 3D Morse crystals

Energy thresholds of discrete breathers in thermal equilibrium and relaxation processes

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