Critical Behavior of the Structure Factor for Higher Harmonics in Density Wave Systems
Abstract
The structure factor Sn\(q\) = <ψn\(q\)ψ*n\(q\)> associated with fluctuations in the nth harmonic density wave (DW) order parameter ψn of a uniaxial system is affected by its bare q dependence, and by the coupling Re\(ψ*nψn1\). The latter involves correlations in the secondary order parameter ψn1, characterized by a correlation length ξn = ξn0[\(T-Tc\)/Tc]-ν, with the same XY model exponent ν for all n, and decaying as q-\(2-ηn\) for large q. For n>1, ηn is large. The ratio Xn = \(ξn0/ξ10\)2 is universal, and X2 = ɛ/20-ɛ2/100+O\(ɛ3\) in d = 4-ɛ. This naturally explains previously puzzling experimental results for S2 at a nematic-smectic- A2 transition. Similar predictions apply for other secondary order parameter correlations.
- Publication:
-
Physical Review Letters
- Pub Date:
- June 1995
- DOI:
- 10.1103/PhysRevLett.74.5064
- Bibcode:
- 1995PhRvL..74.5064A