Smectic blue phases ( ${\mathrm{BP}}_{\mathrm{Sm}}$) are thermotropic liquid crystalline phases which exhibit both three-dimensional orientational order, such as classical blue phases, and smectic positional order. ${\mathrm{BP}}_{\mathrm{Sm}}$ appear as the three-dimensional counterpart of twist grain boundary phases. X-ray scattering and optical polarizing microscopy provide information on the hexagonal and cubic symmetries of these new phases.

• Received 19 October 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.3791