Effective Conductivity due to Continuous Polarization Reorientation in Fluid Ferroelectrics*

In crystal ferroelectrics, the macroscopic polarization density \textbf{P} is stabilized to a set of discrete orientations by the underlying lattice, and ferroelectricity characterized by field-induced switching of \textbf{P} between these stable states. Fluid ferroelectrics exhibit \textbf{P} with no energy barriers to its reorientation. As a result, \textbf{P} can respond to applied electric field in a continuous fashion. We show here that, due to the reorientation of \textbf{P}, an otherwise insulating fluid ferroelectric behaves electrically as a resistive medium, with conductivity in the semiconducting range. Measurements of cell dynamics are reported for the SmAP$_{F}$ material W623, a bent-core liquid crystal (LC) with large macroscopic polarization that we find to exhibit nearly ideal field-induced block polarization reorientation. We have investigated theoretically the dynamic behavior of block polarization in the SmAP$_{F}$ phase, finding that a reorienting LC polarization block behaves electrically as a resistor. Experimental studies of W623 confirm this behavior, revealing the low resistance of the block-reorienting LC and the corresponding characteristic flat-topped step in the current response.