Birefringence investigation of the smectic-A—hexatic-Bphase transition

Abstract

Birefringence measurements of $n$-hexyl 4′-$n$-pentyloxbiphenyl-4-carboxylate (650BC) near the smectic-$A$—hexatic-$B$ transition are reported. It is found that the anomalous part of the birefringence $\delta \left(\Delta n\right)$ due to long-range hexatic order exhibits a critical exponent 0.38 ±0.05. The relationship between $\delta \left(\Delta n\right)$ and the hexatic order parameter is discussed.