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

The low-frequency (ν=10 kHz) dielectric constants and hysteresis loops of BCCD have been measured under hydrostatic pressure ($p<550$ MPa) and at varying temperatures (115 K<T<260 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.