 
Summary: VOLUME 85, NUMBER 18 P H Y S I C A L R E V I E W L E T T E R S 30 OCTOBER 2000
Deviations from Linear Theory for Fluctuations below the Supercritical Primary
Bifurcation to Electroconvection
Michael A. Scherer and Guenter Ahlers
Department of Physics and iQUEST, University of California, Santa Barbara, California 93106
Frank Hörner and Ingo Rehberg
Experimentalphysik V, Universität Bayreuth, D95440 Bayreuth, Germany
(Received 4 May 2000)
Over two decades ago it was predicted that nonlinear interactions between thermally driven fluctuations
in dissipative nonlinear nonequilibrium systems lead to deviations from meanfield theory. Here we report
experimental observations of such deviations as a supercritical primary bifurcation is approached. We
measured the meansquare directorangle fluctuations u2
below the bifurcation to electroconvection of
two different nematic liquid crystals. For emf V2
V2
c,mf 2 1 & 20.1 (V is the applied voltage) we
find u2
~ jemfj2g
with g given by linear theory (LT). Closer to the bifurcation there are deviations
from LT with a smaller g and with V2
