Pattern Formation in Electroconvection of Nematics under Spatially-Periodic Force

Experimental study about pattern selection processes under spatially-periodic external force in the electroconvection system is reported. Specific formation processes of periodic patterns beyond the threshold were observed due to the external forces and wavenumbers. The convection pattern was either entrained into the external periodic force or maintained with the intrinsic spontaneous wavenumber (the fastest growing one), depending on magnitudes of mismatches such as difference between the wavenumber of the entrained pattern and the spontaneous wavenumber. We call it the entrainment (or spatial synchronization) of wave-numbers. The spatial entrainment and desynchronization were investigated in detail by changing applied frequencies and voltages.