 
Summary: RayleighBe´nard convection in a homeotropically aligned nematic liquid crystal
Leif Thomas,1
Werner Pesch,2
and Guenter Ahlers1
1
Department of Physics and Center for Nonlinear Science, University of California at Santa Barbara,
Santa Barbara, California 93106
2
Institut fu¨r Theoretische Physik, Universita¨t Bayreuth, Bayreuth, Germany
Received 22 April 1998
We report experimental results for convection near onset in a thin layer of a homeotropically aligned
nematic liquid crystal heated from below as a function of the temperature difference T and the applied
vertical magnetic field H. When possible, these results are compared with theoretical calculations. The experi
ments were done with three cylindrical cells of aspect ratios radius / height 10.6, 6.2, and 5.0 over the
field range 8 h H/HF 80 (HF 20.9, 12.6, and 9.3 G are the Fre´edericksz fields for the three cells . We
used the Nusselt number N effective thermal conductivity to determine the critical Rayleigh number Rc and
the nature of the transition. We analyzed digital images of the flow patterns to study the dynamics and to
determine the mean wave numbers of the convecting states. For h less than a codimensiontwo field hct 46 the
bifurcation is subcritical and oscillatory, with traveling and standingwave transients. Beyond hct the bifurca
tion is stationary and subcritical until a tricritical field ht 57.2 is reached, beyond which it is supercritical. We
