Multicritical Point and Structure Branching Patterns in the Modulated Phases of Betaine Calcium Chloride Dihydrate (BCCD)

The low-frequency ($\nu =10\mathrm{}$ kHz) dielectric constants and hysteresis loops of BCCD have been measured under hydrostatic pressure ($p<\mathrm{}550\mathrm{}$ MPa) and at varying temperatures ($115 \mathrm{K}<T<\mathrm{}260\mathrm{} \mathrm{K}$). Several new pressure-induced commensurate and incommensurate phases have been detected and interpreted using the anisotropic next-nearest-neighbor Ising model. Structure branching processes with similar topology in different regions of the phase diagram have been observed. The existence of a Lifshitz point in BCCD is suggested.