1999/08/25 by T. Nattermann, Nattermann, T., T. Emig +3
Physics and Astronomy · #FOS: Physical sciences #Statistical Mechanics (cond-mat.stat-mech) #cond-mat.stat-mech
paper · pdf · doi:10.48550/arxiv.cond-mat/9908353
5 pages, 1 figure; to appear in the proceedings of ECRYS-99
arxiv created 1999/08/25 · arxiv updated 2009/11/30
Thermal fluctuations are known to play an important role in low-dimensional systems which may undergo incommensurate-commensurate or (for an accidentally commensurate wavevector) lock-in transitions. In particular, an intermediate floating phase with algebraically decaying correlations exists only in D=2 dimensions, whereas in higher dimensions most features of the phase diagram are mean-field like. Here we will show, that the introduction of frozen-in disorder leads to strong fluctuation effects even in D<4 dimensions. For commensurate wavevectors the lattice pinning potential dominates always over weak impurity pinning if p ≤ pc=6/π(D=3), where p denotes the degeneracy of the commensurate phase. For larger p a disorder driven continuous transition between a long-range ordered locked-in phase and quasi-long-range ordered phase, dominated by impurity pinning, occurs. Critical exponents of this transition, which is characterized by a zero temperature fixed point, are calculated within an expansion in 4-D. The generalization to incommensurate wavevectors will be discussed. If the modulation in the quasi-long-range ordered phase has hexagonal symmetry, as e.g.for flux-line lattices, the algebraic decay is non-universal and depends on the Poisson ratio of the elastic constants. Weakly driven transport is dominated by thermally activated creep in both phases, but with different creep exponents.