Showing papers by "David A. Huse published in 1987"

Dynamics of droplet fluctuations in pure and random ising systems

Abstract: Long-lived droplet fluctuations can dominate the long-time equilibrium dynamics of long-range-ordered Ising systems, yielding nonexponential decay of temporal spin autocorrelations. For the two-dimensional pure Ising model the long-time decay is a stretched exponential, exp(- \ensuremath{\surd}t/\ensuremath{\tau} ), where t is time and \ensuremath{\tau} a correlation time. For systems with quenched random-exchange disorder the spatially averaged correlation decays as a power of time, ${t}^{\mathrm{\ensuremath{-}}x}$, with the exponent x in general being nonuniversal. For systems with quenched random-field disorder the decay is slower still, as exp[-k(lnt${)}^{(d\mathrm{\ensuremath{-}}2)/(d\mathrm{\ensuremath{-}}1)}$], where k is a nonuniversal number and d is the dimensionality of the system. The low-frequency noise from this slow dynamics may be experimentally detectable, as is the analogous noise in spin-glass ordered phases.

Critical dynamics of random-field Ising systems with conserved order parameter.

Abstract: Motivated by recent experiments on critical binary fluid mixtures in porous media, the dynamics of random-field Ising systems with conserved order parameter are considered. In the one-phase regime a new dynamic crossover length ${l}_{x}$ is found: for q\ensuremath{\ll}${q}_{x}$=2\ensuremath{\pi}/${l}_{x}$ the temporal decay of S(q,t) is well approximated by a single exponential whose decay rate is determined by diffusive dynamics, while for q\ensuremath{\gtrsim}${q}_{x}$ the temporal decay has a strongly nonexponential component, reflecting the activated dynamics of this system. As the ordering transition is approached, this dynamic length ${l}_{x}$ diverges as ${l}_{x}$\ensuremath{\sim}exp(c${\ensuremath{\xi}}^{\ensuremath{\psi}}$), where \ensuremath{\xi} is the static correlation length, and the activation free-energy barriers are of order cT${\ensuremath{\xi}}^{\ensuremath{\psi}}$ (T being the temperature and c a nonuniversal constant).