title: Suppression of spatially periodic patterns by dc voltage.
abstract: The effect of superposed dc and ac applied voltages on two types of spatially periodic instabilities in nematic liquid crystals, flexoelectric domains (FD), and electroconvection (EC) was studied. The onset characteristics, threshold voltages, and critical wave vectors were determined. We found that in general the superposition of driving with different time symmetries inhibits the pattern forming mechanisms for FD and EC as well. As a consequence, the onset extends to much higher voltages than the individual dc or ac thresholds. A dc-bias-induced reduction of the crossover frequency from the conductive to the dielectric EC regimes and a peculiar transition between two types of flexodomains with different wavelengths were detected. Direct measurements of the change of the electrical conductivity and its anisotropy, induced by the applied dc voltage component, showed that the dc bias substantially affects both parameters. Taking into account the experimentally detected variations of the conductivity in the linear stability analysis of the underlying nematohydrodynamic equations, a qualitative agreement with the experimental findings on the onset behavior of spatially periodic instabilities was obtained.
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary.
authors.forename: Nándor
authors.initials: N
authors.lastname: Éber
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary.
authors.forename: Péter
authors.initials: P
authors.lastname: Salamon
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary.
authors.forename: Balázs András
authors.initials: BA
authors.lastname: Fekete
authors.affiliation: 100. Yil University, Department of Physics, 650580 Van, Turkey.
authors.forename: Ridvan
authors.initials: R
authors.lastname: Karapinar
authors.affiliation: Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany.
authors.forename: Alexei
authors.initials: A
authors.lastname: Krekhov
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary.
authors.forename: Ágnes
authors.initials: Á
authors.lastname: Buka