Herve M. Carruzzo

Structural probe of a glass-forming liquid: generalized compressibility.

We introduce a structural quantity to probe the glass transition. This quantity is a linear generalized compressibility which depends solely on the positions of the particles. We have performed a molecular dynamics simulation on a glass-forming liquid consisting of a two-component mixture of soft spheres in three dimensions. As the temperature is lowered (or as the density is increased), the generalized compressibility drops sharply at the glass transition, with the drop becoming more and more abrupt as the measurement time increases. At our longest measurement times, the drop occurs approximately at the mode coupling temperature T(C). The drop in the linear generalized compressibility occurs at the same temperature as the peak in the specific heat. By examining the inherent structure energy as a function of temperature, we find that our results are consistent with the kinetic view of the glass transition in which the system falls out of equilibrium. We find no size dependence and no evidence for a second order phase transition, though this does not exclude the possibility of a phase transition below the observed glass transition temperature. We discuss the relation between the linear generalized compressibility and the ordinary isothermal compressibility, as well as the static structure factor.

Viscoelasticity and surface tension at the defect-induced first-order melting transition of a vortex lattice

We show that thermally activated interstitial and vacancy defects can lead to first-order melting of a vortex lattice. We obtain good agreement with experimentally measured melting curve, latent heat, and magnetization jumps for YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. The shear modulus of the vortex liquid is frequency dependent and crosses over from zero at low frequencies to a finite value at high frequencies. We also find a small surface tension between the vortex line liquid and the vortex lattice. (c) 2000 The American Physical Society.

Generalized compressibility in a glass-forming liquid

Abstract We introduce a new quantity to probe the glass transition. This quantity is a linear generalized compressibility which depends solely on the positions of the particles. We have performed a molecular dynamics simulation on a glass-forming liquid consisting of a two-component mixture of soft spheres in three dimensions. As the temperature is lowered, the generalized compressibility drops sharply at the glass transition. Our results are consistent with the kinetic view of the glass transition, but not with an underlying second-order phase transition.

First-order pre-melting transition of vortex lattices

Abstract Vortex lattices in the high-temperature superconductors undergo a first-order phase transition that has thus far been regarded as melting from a solid to a liquid. We point out an alternative possibility of a two-step process in which there is a first-order transition from an ordinary vortex lattice to a soft vortex solid followed by another first-order melting transition from the soft vortex solid to a vortex liquid. We focus on the first step. This pre-melting transition is induced by vacancy and interstitial vortex lines. We obtain good agreement with the experimental transition temperature against field, latent heat, and magnetization jumps for YBa2Cu3O7-[sgrave] and Bi2Sr2CaCu2O8.

Interacting defects in glasses

Abstract We find that recent low-temperature nonequilibrium dielectric experiments indicate that glasses have strongly interacting defects. While many of the features found in the experiments can be explained by the standard model of noninteracting two-level systems, we find that the frequency dependence cannot. Using a Monte Carlo simulation of a nearest-neighbor Ising spin glass, we show that interactions between defects can qualitatively explain the experiments because they lead to the formation of clusters and a hole in the distribution of local fields.