Disorder and excess modes in hard-sphere colloidal systems

Zargar, Rojman; Russo, John; Schall, Peter; Tanaka, Hajime; Bonn, Daniel

doi:10.1209/0295-5075/108/38002

Cited by 16 publications

(19 citation statements)

References 44 publications

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“…This approach has been employed, for instance, in the case of a-thermal jammed system in a previous work 133 , where the effect of structural modifications on the distribution of contact forces was systematically studied. Other recent works [134][135][136][137] have followed this direction, providing a deeper understanding of important properties of materials in their crystalline and amorphous forms. Finally, in Ref.…”

Section: Conclusion and Remarksmentioning

confidence: 99%

Relation of vibrational excitations and thermal conductivity to elastic heterogeneities in disordered solids

2016

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In crystals, molecules thermally vibrate around the periodic lattice sites. Vibrational motions are well understood in terms of phonons, which carry heat and control heat transport. The situation is notably different in disordered solids, where vibrational excitations are not phonons and can be even localized. Recent numerical work has established the concept of elastic heterogeneity: Disordered solids show inhomogeneous local mechanical response. Clearly, the heterogeneous nature of elastic properties strongly influences vibrational and thermal properties, and it is expected to be the origin of anomalous features, including boson peak, vibrational localization, and temperature dependence of thermal conductivity. These are all crucial long-standing problems in material physics, which we address in the present work. We have considered a toy model able to stabilize different states of matter, by introducing an increasing amount of size disorder. The phase diagram generated by Molecular Dynamics simulation encompasses the perfect crystalline state with spatially homogeneous elastic moduli distribution, multiple defective phases with increasing moduli heterogeneities, and eventually a series of amorphous states. We have established clear correlations among heterogeneous local mechanical response, vibrational states, and thermal conductivity. We provide evidence that elastic heterogeneity controls both vibrational and thermal properties, and is a key concept to understand the anomalous puzzling features of disordered solids.

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Section: Conclusion and Remarksmentioning

confidence: 99%

Relation of vibrational excitations and thermal conductivity to elastic heterogeneities in disordered solids

2016

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“…The most striking anomaly in glasses is the deviation from the Debye law which manifests itself as the well-documented excess of lowfrequency modes visible as a peak in the the normalized DOS D(ω)/ω 2 . This effect is widely known as the boson peak anomaly, and is a universal feature in glasses [3], although it has often been observed in crystals as well [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Local inversion-symmetry breaking controls the boson peak in glasses and crystals

2016

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It is well known that amorphous solids display a phonon spectrum where the Debye ∼ ω 2 law at low frequency melds into an anomalous excess-mode peak (the boson peak) before entering a quasilocalized regime at higher frequencies dominated by scattering. The microscopic origin of the boson peak has remained elusive despite various attempts to put it in a clear connection with structural disorder at the atomic/molecular level. Using numerical calculations on model systems, we show that the microscopic origin of the boson peak is directly controlled by the local breaking of centerinversion symmetry. In particular, we find that both the boson peak and the nonaffine softening of the material display a strong positive correlation with a new order parameter describing the local inversion symmetry of the lattice. The standard bond-orientational order parameter, instead, is shown to be a poor correlator and cannot explain the boson peak in randomly-cut crystals with perfect bond-orientational order. Our results bring a unifying understanding of the boson peak anomaly for model glasses and defective crystals in terms of a universal local symmetry-breaking principle of the lattice. arXiv:1601.03879v3 [cond-mat.dis-nn]

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“…Using the experimental input from Zargar et al 21 we can obtain a numerical estimation for the absolute value of the shear modulus of a defective colloidal fcc crystals with vacancies. Two examples of configurations with a low (c = 0.0167) and high (c = 0.169) vacancy concentration are shown in Fig.…”

Section: Application To Colloidal Crystalsmentioning

confidence: 99%

Non-affine lattice dynamics of defective fcc crystals

2017

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The mechanical, thermal and vibrational properties of defective crystals are important in many different contexts, from metallurgy and solid-state physics to, more recently, soft matter and colloidal physics. Here we study two different models of disordered fcc crystal lattices, with randomly-removed bonds and with vacancies, respectively, within the framework of non-affine lattice dynamics. We find that both systems feature the same scaling of the shear modulus with the newly defined inversion-symmetry breaking (ISB) parameter, which shows that local inversion-symmetry breaking around defects is the universal root source of the non-affine softening of the shear modulus. This finding allows us to derive analytical relations for the non-affine (zero-frequency) shear modulus as a function of vacancy concentration in excellent agreement with numerical simulations. Nevertheless, due to the different microstructural disorder, the spatial fluctuations of the local ISB parameter are different in the vacancy and bonddepleted case. The vacancy fcc exhibits comparatively a more heterogenous microstructural disorder (due to the broader distribution of coordination number Z), which is reflected in a different scaling relation between boson peak frequency in the DOS and the averageZ. These differences are less important at low vacancy concentrations, where the numerical DOS of the vacancy fcc can be well described theoretically by coherent-potential approximation, presented here for the bond-depleted fcc lattice in 3d.

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Disorder and excess modes in hard-sphere colloidal systems

Cited by 16 publications

References 44 publications

Relation of vibrational excitations and thermal conductivity to elastic heterogeneities in disordered solids

Relation of vibrational excitations and thermal conductivity to elastic heterogeneities in disordered solids

Local inversion-symmetry breaking controls the boson peak in glasses and crystals

Non-affine lattice dynamics of defective fcc crystals

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