Critical Behavior of the Structure Factor for Higher Harmonics in Density Wave Systems
Abstract
The structure factor S_{n}\(q\) = <ψ_{n}\(q\)ψ^{*}_{n}\(q\)> associated with fluctuations in the nth harmonic density wave (DW) order parameter ψ_{n} of a uniaxial system is affected by its bare q dependence, and by the coupling Re\(ψ^{*}_{n}ψ^{n}_{1}\). The latter involves correlations in the secondary order parameter ψ^{n}_{1}, characterized by a correlation length ξ_{n} = ξ_{n0}[\(TT_{c}\)/T_{c}]^{ν}, with the same XY model exponent ν for all n, and decaying as q^{\(2ηn\)} for large q. For n>1, η_{n} is large. The ratio X_{n} = \(ξ_{n0}/ξ_{10}\)^{2} is universal, and X_{2} = ɛ/20ɛ^{2}/100+O\(ɛ^{3}\) in d = 4ɛ. This naturally explains previously puzzling experimental results for S_{2} at a nematicsmectic A_{2} 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