Pattern formation of chevrons in the conduction regime in homeotropically aligned liquid crystals

We report on chevrons (herringbonelike patterns) observed in homeotropicall y aligned liquid crystals with high electric conductivity. We focus our att ention on two types of chevrons observed in the conduction regime. The thre shold voltage and the characteristic double periodicity of chevrons (i.e., the short wavelength lambda(1) of the striated rolls and the long wavelengt h lambda(2) Of the chevron bands) have been measured as functions of the ap plied electric frequency f. With the aid of a crossed polarizer set, we hav e, in addition, determined the director field which shows a periodic in-pla ne rotation for our chevrons (with a wavelength lambda(2)) We arrived at th e types of chevrons after qualitatively different bifurcation sequences wit h increasing voltage. The frequency dependence of lambda(2) also shows a qu alitatively different behavior with respect to the two types of chevrons. T he experimental results are discussed in terms of recent theoretical invest igations.