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In order to test theoretical concepts on the glass transition, we investigate several models of glassy materials by means of Monte Carlo (MC) and Molecular Dynamics (MD) computer simulations. It is shown that also simplified models exhibit a glass transition which is in qualitative agreement with experiment and that thus such models are useful to study this phenomenon. However, the glass transition...
The relevance of studies on orientational and/or rotationally disordered crystals is discussed within the context of glass-forming and other systems exhibiting the basic aspects of glassy behaviour.
We present the dynamics of A1C60 compounds as investigated by inelastic neutron scattering using Rb1C60 as example. Special emphasis is given to the influence of disorder on the dynamical response in the various phases. In the high-temperature fcc phases we find hardly any differences in the dynamics between Rb1C60 compounds and pristine C60, i.e. we observe the typical signatures of a plastic crystal...
Using a molecular dynamics computer simulation we investigate the dynamics of a supercooled binary Lennard-Jones mixture. At low temperatures this dynamics can be described very well by the ideal version of mode-coupling theory. In particular we find that at low temperatures the diffusion constants show a power-law behavior, that the intermediate scattering functions obey the time temperature superposition...
Analyzing recent molecular dynamics simulations in deeply supercooled liquid states, we have found that the single particle dynamics in water can be interpreted in terms of Mode Coupling Theory, in its so-called ideal formulation. In this paper we review such evidence and discuss the relevance of this finding for the debated thermodynamic behavior of supercooled water. The experimental apparent power-law...
The glass transition in a hard sphere system is studied numerically, using a model free energy functional that exhibits glassy local minima at sufficiently high densities. The numerical methods used in our work include free-energy minimization, direct integration of Langevin equations and Monte Carlo simulation. At relatively low densities, the system is found to fluctuate near the uniform liquid...
In these lectures I will study some properties that are shared by many glassy systems. I will shown how some of these properties can be understood in the framework of the mean field approach based on the replica method and I will discuss which are the difficulties which we have to face when we apply the replica method to realistic short range models. We finally present a partially successfully application...
In this talk I review some recent developments which shed light on the main connections between structural glasses and mean-field spin glass models with a discontinuous transition. I also discuss the role of quantum fluctuations on the dynamical instability found in mean-field spin glasses with a discontinuous transition. In mean-field models with pairwise interactions in a transverse field it is...
The glass transition is considered within two toys models, a mean field spin glass and a directed polymer in a correlated random potential. In the spin glass model there occurs a dynamical transition, where the the system condenses in a state of lower entropy. The extensive entropy loss, called complexity or information entropy, is calculated by analysis of the metastable (TAP) states. This...
An analytically tractable model is introduced which exhibits both, a glass-like freezing transition, and a collection of double-well configurations in its zero-temperature potential energy landscape. The latter are generally believed to be responsible for the anomalous low-temperature properties of glass-like and amorphous systems via a tunneling mechanism that allows particles to move back and forth...
We discuss the large scale effective potential for elastic objects in the presence of a random pinning potential. In the static approach, converging analytical results show that the large scale, low temperature free energy landscape consists in a succession of parabolic wells of random depth, matching on singular points where the effective force is discontinuous. These parabolas are themselves subdivided...
This is a short review of the current state of theory and experiment on the structure of elastic lattices weakly interacting with underlying random background. Examples are flux lattices in superconductors, magnetic bubble lattices in ferromagnetic films, charge density waves in semiconductors, and atomic monolayers physisorbed on random surfaces. We shall argue that the orientational order in these...
We discuss numerical experiments that allow to detect an ultrametric structure of the phase space of the 4D spin glasses with quenched random couplings J=±1. We discuss a constrained Monte Carlo method, and systematic problems like finite size effects. We compare our results to the ones we obtain for the mean field Sherrington Kirkpatrick model and by using unconstrained numerical simulations, and...
We discuss the results of recent Monte Carlo simulations of a short range spin glass model with four-spin interactions, in connection with the physics of glasses. The model could be classified as a fragile glass, displaying stretched exponential relaxation with super-Arrhenius behavior of the relaxation time. The growth of this at low temperature appears to be associated to an entropy reduction according...
We give a brief review on a family of two dimensional models with continuous symmetry and possibly regular frustration or frustration-type disorder. Next we focus on the random ± J bond XY model. There are two types of variables in this system and thus two candidates for an order parameter, the continuous spin variable and the discrete chiral variable. The question is : do the chiralities order more...
We discuss a recent mapping of the Anderson-Mott metal-insulator transition onto a random field magnet problem. The most important new idea introduced is to describe the metal-insulator transition in terms of an order parameter expansion rather than in terms of soft modes via a nonlinear sigma model. For spatial dimensions d>dc+=6 a mean field theory gives the exact critical...
Ising spin glasses in a transverse field exhibit a zero temperature quantum phase transition, which is driven by quantum rather than thermal fluctuations. They constitute a universality class that is significantly different from the classical, thermal phase transitions. Most interestingly close to the transition in finite dimensions a quantum Griffiths phase leads to drastic consequences for various...
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