Spontaneous helix formation in a polar smectic phase.

In soft ferroelectric crystals, the depolarization field can be reduced by a periodic distortion of the polarization direction. In the polar nematic and tilted smectic phases, this process is energetically favored, as it only requires changes in the director orientation. We demonstrate the spontaneous formation of a helical structure in the proper ferroelectric tilted smectic (SmCHP) phase, formed below the heliconical polar nematic (N) phase. The helical pitch in the smectic phase is approximately 600 nm and remains nearly constant across the entire temperature range of the phase. Under weak electric field, the helix reorients while its structure remains largely intact; however, in stronger field the helix is destroyed as the electric polarization aligns along the electric field.