Abstract:
This paper reports on measurements with a high-accuracy universal polarimeter of the optical activity of tetramethylammonium tetrachloro-zincate. This compound has an incommensurately modulated phase that is centrosymmetric if one averages the effect of the modulation. Therefore, the question arises whether this phase is optically active or not. For the three components of the gyration tensor (g(11), g(13), and g(33)) that have been measured with a thoroughly tested setup, we present results which were always zero. On the contrary, results reported by others are clearly nonzero. The possible reasons for this controversy are discussed.