D. Kaya, N. L. Green, C. E. Maloney, and M. F. Islam, Science 329 , 656 (2010).
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Disordered Solids Mohammad F. Islam, Carnegie Mellon University, DMR 0645596 The normal modes and the density of states (DOS) of any material provide a framework for understanding its thermal and mechanical transport properties. In perfect crystals, normal modes take the form of planewaves. In disordered systems, they can be complex. We have recently experimentally measured the normal modes and the DOS in a disordered colloidal crystal composed of deformable microgel particles. The DOS shows Debye-like behavior at low energies and an excess of modes, a so-called boson peak, at higher energies. The normal modes take the form of planewaves hybridized with localized short-wavelength features in the Debye regime. Our results establish that Debye-like behavior at low energies with an excess of modes at higher energies are generic features of disordered solids. a, N. L. Green, C. E. Maloney, and M. F. Islam, Science 329, 656 (2010). Figure 2: Normalized mode vectors along with the squared amplitude of the projection onto transverse and longitudinal plane waves. Figure 1: Reduced DOS.
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Normal Modes and Density of States of Disordered Solids Mohammad F. Islam, Carnegie Mellon University, DMR 0645596. - PowerPoint PPT Presentation
Transcript of D. Kaya, N. L. Green, C. E. Maloney, and M. F. Islam, Science 329 , 656 (2010).
Normal Modes and Density of States of Disordered Solids
Mohammad F. Islam, Carnegie Mellon University, DMR 0645596
The normal modes and the density of states (DOS) of any material provide a framework for understanding its thermal and mechanical transport properties. In perfect crystals, normal modes take the form of planewaves. In disordered systems, they can be complex. We have recently experimentally measured the normal modes and the DOS in a disordered colloidal crystal composed of deformable microgel particles. The DOS shows Debye-like behavior at low energies and anexcess of modes, a so-called boson peak, at higher energies. The normal modes take the form of planewaves hybridized with localized short-wavelength features in the Debye regime. Our results establish that Debye-like behavior at low energies with an excess of modes at higher energies are generic features of disordered solids.
D. Kaya, N. L. Green, C. E. Maloney, and M. F. Islam, Science 329, 656 (2010).
Figure 2: Normalized mode vectors along with the squared amplitude of the projection onto transverse and longitudinal plane waves.
Figure 1: Reduced DOS.
Disordered crystals are often used as a simple theoretical framework to understand generic emergent behavior in other types of disordered systems, such as structural glasses. Our approach will be an important tool to identify the impacts, at a particle-scale level, of different types of disorder on the structure of the normal modes and elasticity that are present in various atomic, molecular, and colloidal crystals and glasses.
A graduate student (Nicole Green) and a postdoctoral researcher (Deniz Kaya) participated in this project. In addition, three undergraduate students were also involved in this work (John Berezney, currently a graduate student at UCSB; Harry An, currently a graduate student at MIT; Zachary Bryan, currently a graduate student at Florida).
Zachary Bryan received best undergraduate research award in 2008 from NSF funded CMU –REU.
Graduate student Nicole Green and PI looking at a colloidal crystal sample.
Normal Modes and Density of States of Disordered Solids
Mohammad F. Islam, Carnegie Mellon University, DMR 0645596
