Optical birefringence in the incommensurate phase of {N(CH3) 4}2ZnCl4

Abstract
The optical birefringence of { N(CH3)4 }2ZnCl 4 has been measured. Below T0, the exponent of its temperature dependence is identified to 2 - α - Φ = 0.87 ± 0.02. The lock-in transition is observed, exhibiting an hysteresis of about 0.25°. These data are compared with the predictions of Mashiyama's theory