Splay State Research Articles

Splay states in globally coupled Josephson arrays: Analytical prediction of Floquet multipliers.

In recent numerical experiments on series arrays of overdamped Josephson junctions, Nichols and Wiesenfeld [Phys. Rev. A 45, 8430 (1992)] discovered that the periodic states known as splay states are neutrally stable in all but four directions in phase space. We present a theory that accounts for this enormous degree of neutral stability. The theory also predicts the four non-neutral Floquet multipliers to within 0.1% of their numerically computed values. The analytical approach used here may be appli- cable to other globally coupled systems of oscillators, such as multimode lasers, electronic oscillator circuits, and solid-state laser arrays.

Surface Transition in a Nematic Layer with Reverse Pretilt

Abstract Recently, a surface induced transition from homeotropic to planar alignment in a nematic layer and the corresponding optical response has been reported/K. Flatischler, L. Komitov, S. T. Lagerwall, B. Stebler, and A. Strigazzi, Mol. Cryst. Liq. Cryst., 198, 119 (1991)/. In the case of surface conditions with reverse pretilt a similar transition from quasi-homeotropic bent alignment to quasi-planar splayed state can be obtained. As known, these two states are topologically incompatible, and therefore the transition is accompanied by nucleation of π-disclination lines, and even is reversible, it exhibits a big hysteresis. Moreover, it can be driven not only by temperature but also by an applied electric field, using a nematic with negative dielectric anisotropy. A simple theoretical description of such an alignment transition is presented.