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 QZ, 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