New classification of chevrons in electroconvection in homeotropically-aligned nematics

Two types of chevrons have been found in the conduction regime, as well as the conventional chevrons in the dielectric regime in homeotropically-aligned nematics. These two are named the defect-mediated chevron (DMC) and the defect-free chevron (DFC) by their structure changes. Two different bifurcation sequences are found with increasing the applied voltage, such as Fréedericksz transition → normal rolls → abnormal rolls → defect chaos →DMC for low frequencies and Fréedericksz transition → prewavy pattern → DFC for high frequencies. Moreover, the double periodicity of the chevrons (i.e., the short wavelength λ₁ of the striated rolls and the long wavelength λ₂ of the chevron bands) shows quite specific frequency dependence.