Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q18: Disordered and Glassy Systems I |
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Sponsoring Units: DCMP GSNP Chair: Alexei Sokolov, University of Tennessee/Knoxville Room: 403 |
Wednesday, March 5, 2014 2:30PM - 2:42PM |
Q18.00001: Random matrix definition of the boson peak M. Lisa Manning, Andrea J. Liu The density of vibrational states for glasses and jammed solids exhibits universal features, including an excess of modes above the Debye prediction known as the boson peak, located at a frequency $\omega^*$. We show that the eigenvector statistics for modes in the boson peak are universal and emerge from the interplay of disorder and global translation invariance in the dynamical matrix. We demonstrate that a very large class of random matrices contains a band of modes with this same universal structure, and conjecture the existence of a new universality class. We characterize the eigenvector statistics as a function of coordination number, and find that one member of this new class reproduces the scaling of $\omega^{*}$ with coordination number that is observed near the jamming transition. [Preview Abstract] |
Wednesday, March 5, 2014 2:42PM - 2:54PM |
Q18.00002: A New Method for Identifying Defects in Disordered Solids Sven Wijtmans, Lisa Manning Characterizing defects in solids is an important step to developing continuum equations for failure in materials. Defects in crystalline solids (i.e. dislocations) are easy to characterize, but in disordered solids the lack of crystalline order makes it difficult to identify where particle rearrangements are likely to occur. Recently, vibrational modes have been used to identify flow defects or ``soft spots'' in disordered solids. However, the algorithm contains several free parameters that are difficult to constrain and does not provide detailed information about the nature of the defects. Here we describe a new method for identifying defects. We add spring-like interactions between coarse-grained grid points, thereby suppressing long-wavelength sound modes. This allows us to identify the energy barriers and precise displacements corresponding to defects, and potentially avoids systematic effects generated by elastic interactions between defects. Plastic events do occur at defect locations, and are correlated with the defect energy barriers. We find that the energy barriers of defects are significantly lower that the energy barriers for the eigenvectors. [Preview Abstract] |
Wednesday, March 5, 2014 2:54PM - 3:06PM |
Q18.00003: Topological Defects by Size Polydispersity Zhenwei Yao, Monica Olvera de la Cruz The engineering of defects in crystalline matter introduces entirely new physical properties of materials. The fascinating possible applications of defects, known as topological defects, provide great motivations to perform fundamental investigations to uncover their role on the physical properties of various systems. Here we investigate topological defects in size polydispersity on flat surfaces. Our simulations show that in polydispersed systems topological defects play the role of order-restoring. The perfect hexagonal lattice beyond a small defective region around the impurity particle is well protected. Moreover, size polydispersity is shown numerically here to be an essential ingredient to understand short-range attractions between like-charge disclinations. Our study suggests the promising potential of size polydispersity to engineer defects in real systems. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:18PM |
Q18.00004: Origin of Rigidity in Dry Granular Solids Sumantra Sarkar, Bulbul Chakraborty In traditional solids, the resistance to shear is associated with broken translational symmetry as exhibited by a nonuniform density pattern. In this talk, we show that the emergence of shear rigidity in granular solids is a collective process, which is controlled solely by boundary forces, the constraints of force and torque balance, and the positivity of the contact forces, and not energetic or entropic considerations. We present a theoretical framework that connects rigidity to broken translational symmetry in a reciprocal space representing contact forces. We apply our theory to experimentally generated shear-jammed states and show that these states are indeed characterized by a persistent, non-uniform density modulation in force space, which emerges at the shear-jamming transition\footnote{ Sumantra Sarkar et al, Phys. Rev. Lett. 111, 068301}. Crucial to these analyses was an algorithm that was developed to obtain the reciprocal space structures for any real space configuration under mechanical equilibrium. Also, this algorithm help us identify the source of plastic failure which leads to avalanches in these systems. We argue that continuum theories of granular solidification and response should be based on the reciprocal space picture. [Preview Abstract] |
Wednesday, March 5, 2014 3:18PM - 3:30PM |
Q18.00005: Role of Temperature on Self-organization of Networks Le Yan, Matthieu Wyart Both the thermodynamics and the dynamics of network glasses strongly depend on the network coordination. For instance, the fragility and the jump of specific heat at glass transition of covalent glass are minimal when the covalent network sits at the rigidity transition. We introduced a random network model with frozen topology to rationalize these observations (Yan, D\"urning, Wyart, PNAS(2013)). Here, we consider a novel model without frozen disorder, where the network topology can change dynamically. The model and the previous one shows nearly identical thermodynamic properties. In addition, this model allows us to compare rigidity percolation and jamming, and to study the presence of a rigidity window in covalent glasses. [Preview Abstract] |
Wednesday, March 5, 2014 3:30PM - 3:42PM |
Q18.00006: Elastic Instability and Sound Dispersion in Amorphous Solids Eric DeGiuli, Adrien Laversanne-Finot, Gustavo During, Edan Lerner, Matthieu Wyart Connectedness and applied stress are key characteristics of amorphous solids at zero temperature. Rigidity can be lost either through unjamming as connectedness is decreased, or buckling as stress is increased. We present an effective medium theory which describes elastic behaviour in proximity to both unjamming and buckling. The theory successfully predicts (i) the dependence of the boson peak on pressure and coordination, (ii) negative sound dispersion and a kink in sound attenuation near the boson peak, as observed experimentally in molecular glasses, (iii) a characteristic frequency $\omega_0$ that vanishes at a critical pressure, and (iv) the previously derived stability diagram for $T=0$ amorphous solids. Our predictions for sound dispersion are similar to disorder-based approaches to the boson peak, however we resolve two inconsistencies of these approaches: (i) since disorder is secondary to connectedness and stress in our theory, we explain why some crystals and glasses have similar elasticity, and (ii) we explain the natural emergence of a mesoscopic length scale visible in response, which is absent in static structure. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q18.00007: Glassy Dynamics and Anomalous Diffusion in Self-Assembled Nanoparticle Monolayers Leandra Boucheron, Jacob Stanley, Yeling Dai, Sean You, Binhua Lin, Mati Meron, Suresh Narayanan, Alec Sandy, Zhang Jiang, Oleg Shpyrko We experimentally investigate the structure and dynamics of iron oxide nanoparticle thin films self-assembled at the liquid-air interface. Upon deposition on a water surface and subsequent lateral compression, iron oxide nanoparticles coated with oleic acid ligands self-assemble into a morphologically uniform quasi-2D monolayer. We examined the in-plane structure of these self-assembled films using Grazing-Incidence X-Ray Diffraction (GIXD) and investigated the interparticle dynamics using X-Ray Photon Correlation Spectroscopy (XPCS). The logarithmic relaxation of the surface pressure of the films post-compression suggests the presence of glassy dynamics in the system. Autocorrelation functions derived from XPCS measurements quantify the characteristic timescale of such dynamics and have been fit using the Kohlrausch-Williams-Watts (KWW) model to extract the degree of glassiness. Finally, the q-dependence of the interparticle dynamics in the films is supportive of an anomalous diffusion regime, $\langle x^{2}\rangle \propto t^{n}$, with $n>1$. I will discuss these results and their implications with regards to the nanoscale interactions involved in thin film self-assembly and rearrangement. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q18.00008: Melting Scenario for Coulomb-interacting Classical Particles in Two-dimensional Irregular Confinements Dyuti Bhattacharya, Amit Ghosal We report the thermal ``melting'' of self-formed rigid structures made of a small number of interacting classical particles in two-dimensional confined geometries. We will focus on the role of irregularities of the confinement on the melting of these Coulomb-interacting particles using Monte Carlo simulations. It will be shown that the interplay of long-range Coulomb repulsions between these particles and the irregular confinement yields a solid-like phase (termed as irregular Wigner molecules) at low temperatures that possesses a bond-orientation order. However, the positional order is depleted even at the lowest temperatures due to the disordered confinement. Upon including thermal fluctuations, this solid-like phase smoothly crosses over to a liquid-like phase by destroying the bond-orientation order. This cross-over will be demonstrated by the temperature dependence of several physical observables. The collapse of the solidity will be shown to be defect mediated, and aided primarily by the proliferation of free disclinations, initiated by intriguing tortuous path of correlated fluctuations. These results will help us quantifying the melting found in experiments on systems with confined geometries. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q18.00009: Efficient simulation scheme for studying spin-glass transitions Cheng-Wei Liu, Anatoli Polkovnikov, Anders W. Sandvik We propose and demonstrate an efficient simulation scheme for studying spin-glass transitions. This method is based on the idea of approaching the transition point through a non-equilibrium quench process, formally known as Kibble-Zurek mechanism. Recent studies have shown that there exists dual scaling behavior as a function of quench velocity. This dual scaling behavior allows us to extract transition point, static critical exponents as well as dynamic exponents to good numerical accuracy with an efficient computational effort. We have tested this approach with anti-ferromagnetic Ising model on 3-regular random graphs in terms of both classical and quantum phase transitions and we have obtained good agreement with known results. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q18.00010: Avalanches and hysteresis in frustrated superconductors and $XY$ spin-glasses Auditya Sharma, Alexei Andreanov, Markus Mueller We study avalanches along the hysteresis loop of long-range interacting spin-glasses with continuous XY symmetry - which serves as a toy model of granular superconductors with long-range and \ frustrated Josephson couplings. We identify sudden jumps in the $T=0$ configurations of the XY phases, as an external field is increased. They are initiated by the softest mode of the inverse\ susceptibility matrix becoming unstable, which induces an avalanche of phase updates (or spin alignments). We analyze the statistics of these events, and study the correlation between the no\ n-linear avalanches and the soft mode that initiates them. We find that the avalanches follow the directions of a small fraction of the softest modes of the inverse susceptibility matrix, sim\ ilarly as was found in avalanches in jammed systems. In contrast to the similar Ising spin-glass (Sherrington-Kirkpatrick) studied previously, we find that avalanches are not distributed with\ a scale-free power law, but rather have a typical size which scales with the system size. [Preview Abstract] |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q18.00011: Local activated dynamics in liquids Takuya Iwashita, Takeshi Egami Transport properties of glass-forming liquids, such as viscosity and diffusion, are an important and unsolved subject in condensed matter physics, and in particular the quantitative description of the dynamics of such liquids still remains incomplete. We studied the local activation process in a liquid in terms of the change in local coordination number Nc, which is the number of nearest neighbor atoms. We calculated the transition rate between Nc coordinated state and (Nc+1) or (Nc-1) coordinated state in 3D molecular dynamics simulation. The transition rate is dependent on Nc, and as temperature is lowered the transition rate exhibits a strong dependence on Nc, indicating the system becomes more heterogeneous at the atomic level. The analysis allows us to determine local activation energy as a function of temperature and Nc, and in Nc-configuration space a local energy landscape picture was constructed as a new conceptual view of liquid dynamics. This result provides an interesting and fundamental framework for describing the dynamics of liquids. We also discuss the principle of detailed balance for the transition rate in liquids. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q18.00012: A free-energy surface exploration algorithm for supercooled liquids and amorphous solids Kirk D. Lewis, Yongwoo Shin, Xi Lin Efficient exploration of the multidimensional free-energy surfaces (FES) of supercooled liquids and amorphous solids at low temperatures is extremely challenging. The recently developed autonomous basin-climbing (ABC) algorithm (JCP 130: 224504, 2009) allows the sluggish system to self-explore the multidimensional potential energy surface (PES) and climb out of deep energy basins through a series of collective activation and relaxation events. In this work, we present a new FES exploration algorithm that enforces an explicit temperature dependence on the ABC trajectories. The explicit temperature dependence is achieved by introducing an ensemble of walkers to collectively maintain the detailed balance criteria among all the relevant energy basins. Using this new algorithm, the metabasin correlation length of a binary Lennard-Jones supercooled liquid is identified at the glass transition temperature. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:06PM |
Q18.00013: Microsecond molecular dynamics simulations of stress relaxation and slow quench in silica melts and glasses J. Matthew D. Lane Quench rates and stress relaxation in molecular dynamics simulations of glasses are usually studied on time-scales which are many orders of magnitude faster that those in experiment. We present results from relaxation of hydrostatic compressive stress in silica glass using classical molecular dynamics simulations. Structural variation will be discussed as a function of quench rate for glasses quenched 2 to 3 orders of magnitude slower than previously reported. Stress relaxation curves plotted in log t show time-temperature superposition holds over a wide-range of temperatures for 3\% initial volume compression. Silica melts and glasses were modeled with the BKS interatomic potential and were produced through a melt-quench process. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, March 5, 2014 5:06PM - 5:18PM |
Q18.00014: Modeling vitreous silica bilayers Avishek Kumar, Mark Wilson, David Sherrington, Michael Thorpe The recent synthesis and imaging of bilayers of vitreous silica has led to a wealth of new information [1-2]. We have modeled the experimentally-observed bilayer using a computer assembly procedure [3] to form a network of corner-sharing tetrahedra, which is then mirror-reflected to form a bilayer. We show that the vitreous silica bilayer has additional macroscopic degrees of freedom iff there is a symmetry plane through the center of the bilayer going through the central layer of oxygen ions that join the upper and lower monolayers. We have computer-refined the experimental coordinates to determine the density, and other structural characteristics such as the Si-Si pair distribution function, Si-O-Si bond angle distribution and the Aboav-Weaire law. [1] P. Y. Huang, S. Kurasch, A. Srivastava, V. Skakalova, J. Kotakoski,A. V. Krasheninnikov, R. Hovden, Q. Mao, J. C. Meyer, J. Smet,D. A. Muller, and U. Kaiser, Nano. Lett. 12, 1081 (2012). [2] M. Heyde, S. Shaikhutdinov, and J. J. Freund, Chem. Phys. Lett.550, 1 (2012). [3] M. Wilson, A. Kumar, D. Sherrington, M.F. Thorpe, Phys. Rev. B (87) 214108 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 5:18PM - 5:30PM |
Q18.00015: Plasticity, defect dynamics and superfluid phenomena in deformed solid $^4$He Debabrata Sinha, Surajit Sengupta, Chandan Dasgupta, Oriol Valls We present a numerical study of a continuum plasticity field coupled to a Ginzburg-Landau model for superfluidity. The results suggest that a supersolid fraction may appear as a long-lived transient during the time evolution of the plasticity field at higher temperatures where both dislocation climb and glide are allowed. Supersolidity, however, vanishes with annealing. As the temperature is decreased, dislocation climb is arrested and any residual supersolidity due to incomplete annealing remains frozen. We show that superfluid response will be experimentally observable only if certain mechanical and structural conditions are satisfied. Study of the superfluid phenomena in solid $^4$He in the presence of a dynamic defect density gives rise to many interesting observations and may provide a resolution to some of the perplexing issues concerning a variety of experiments on bulk solid $^4$He. [Preview Abstract] |
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