Resonant X-Ray Diffraction Study of an Unusually Large Phase Coexistence in Smectic Liquid-Crystal Films

The recent discovery of the new smectic-C*(d6) (SmC*(d6)) phase [S. Wang et al., Phys. Rev. Lett. 104, 027801 (2010)] also revealed the existence of a noisy region in the temperature window between the SmC*(d6) phase and the smectic-C*(d4) (SmC*(d4)) phase. Characterized by multiple resonant peaks spanning a wide region in Q(Z), the corresponding structure of this temperature window has been a mystery. In this Letter, through a careful resonant x-ray diffraction study and simulations of the diffraction spectra, we show that this region is in fact an unusually large coexistence region of the SmC*(d6) phase and the SmC*(d4) phase. The structure of the noisy region is found to be a heterogeneous mixture of local SmC*(d6) and SmC*(d4) orders on the sub-mu m scale.