arXiv subjects

T. Emig

Publications and source records attributed to T. Emig.

22 records · Page 2Linked to original sources

arXiv2006

Casimir interaction between a plate and a cylinder

We find the exact Casimir force between a plate and a cylinder, a geometry intermediate between parallel plates, where the force is known exactly, and the plate--sphere, where it is known at large separations. The force has an unexpectedly weak decay \sim L/(H^3 \ln(H/R)) at large plate--cylinder separations H (L and R are the cylinder length and radius), due to transverse magnetic modes. Path integral quantization with a partial wave expansion additionally gives a qualitative difference for the density of states of electric and magnetic modes, and corrections at finite temperatures.

cond-mat.stat-mech↗

arXiv2001

Comment on "A Bragg glass phase in the vortex lattice of a type II superconductor"

In a recent letter Klein et al. [Nature 413, 404 (2001); cond-mat/0110018] provide experimental evidence for the existence of the Bragg glass phase in impure type II superconductors. Here we show that a more complete consideration of recent theoretical findings allows an even better interpretation of the experimental data.

cond-mat.supr-con↗

arXiv2000

Nonuniversal Correlations and Crossover Effects in the Bragg-Glass Phase of Impure Superconductors

The structural correlation functions of a weakly disordered Abrikosov lattice are calculated in a functional RG-expansion in $d=4-ε$ dimensions. It is shown, that in the asymptotic limit the Abrikosov lattice exhibits still quasi-long-range translational order described by a {\it nonuniversal} exponent $η_{\bf G}$ which depends on the ratio of the renormalized elastic constants $κ={c}_{66}/ {c}_{11}$ of the flux line (FL) lattice. Our calculations clearly demonstrate three distinct scaling regimes corresponding to the Larkin, the random manifold and the asymptotic Bragg-glass regime. On a wide range of {\it intermediate} length scales the FL displacement correlation function increases as a power law with twice the manifold roughness exponent $ζ_{\rm RM}(κ) $, which is also {\it nonuniversal}. Correlation functions in the asymptotic regime are calculated in their full anisotropic dependencies and various order parameters are examined. Our results, in particular the $κ$-dependency of the exponents, are in variance with those of the variational treatment with replica symmetry breaking which allows in principle an experimental discrimination between the two approaches.

cond-mat.supr-con↗

arXiv1999

Disorder Driven Lock-In Transitions of CDWs and Related Structures

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 \le p_c=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.

cond-mat.stat-mech↗