Resonant x-ray diffraction study of an unusually large phase coexistence in smectic liquid-crystal films

The recent discovery of the new smectic-Cd6* (SmCd6*) phase also revealed the existence of a noisy region in the temperature window between the SmCd6* phase and the smectic-Cd4* (SmCd4*) 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 SmCd6* phase and the SmCd4* phase. The structure of the noisy region is found to be a heterogeneous mixture of local SmCd6* and SmCd4* orders on the sub-μm scale.