Dielectric Relaxation under DC Field in an Antiferroelectric Liquid Crystal MHPOCBC

Linear and nonlinear dielectric measurements under dc electric fields have been performed in an antiferroelectric liquid crystal MHPOCBC to obtain a deeper insight of dynamic properties related to a field-induced phase, designated as SmCX*, appearing when subjected to electric fields in the SmC alpha* phase. We observed a tricritical point in the SmC alpha*-SmCX* phase transition. We found two low frequency modes coming from domain walls in the first-order phase transitions to SmCX* and to SmC. In the third-order nonlinear dielectric measurements another low frequency mode was observed, of which frequency decreases near the SmC alpha*-SmCX* transition point. This may be the soft mode responsible for the field-induced transition.