Title

Nonequilibrium dynamics of driven elastic manifolds in random media

Date of Award

1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor(s)

M. Cristina Marchetti

Keywords

overdamped, depinning transition, condensation

Subject Categories

Condensed Matter Physics

Abstract

Different aspects of the overdamped dynamics of elastic manifolds driven through random media have been studied. It is known that at zero temperature such systems typically exhibit a continuous depinning transition at a threshold force $F\sb{T}$ from a pinned state with zero average velocity, $< v >$ = 0, for F $<$ $F\sb{T}$, to a sliding state with nonzero average velocity, $< \nu \not= 0 >$, for $F > F\sb{T}$. Using the example of an elastic interface driven in (l + l)-dimensions, we study (1) the effect of finite temperature on the depinning transition, and (2) the T = 0 dynamics at $F \ll F\sb{T}$ where the interface moves from one pinned state to another in response to a small increment in the driving force. We find in (1) that the depinning transition is smeared out by thermal fluctuations, and in (2) that the T = 0 dynamics at $F < F\sb{T}$ is composed of a sequence of discharging events, or avalanches, whose distribution in size has a power-law decay. We also study the finite temperature dynamics at small driving forces, $F \ll F\sb{T}$, and find a nonlinear glassy response for the driven medium, $< v > \sim \exp(-{\rm const} \times F\sp{-\mu}$). Finally, motivated by recent theoretical and experimental work on driven flux-line lattices in type-II superconductors which suggest that the disorder becomes less relevant at large driving forces, we study the $T = 0$ driven dynamics of a sliding charge-density wave (CDW) at $F \ll F\sb{T}$. The CDW model is chosen here because, while it captures all the essential features of the dynamics of driven elastic manifolds, it is simpler than flux-line lattices in that the dynamical field of interest is a scalar rather than a vector. The sliding CDW exhibits a first order dynamical transition at a critical driving force $F\sb{c}$ between "rough" (disorder dominated) $(F < F\sb{c})$ and "flat" $(F > F\sb{c})$ sliding phases, where disorder is washed out by the external drive.

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