P. Sonntag et al., Critical behavior of the de Gennes elastic constants near the nematic-smectic-A transition of TBBA, PHYS REV L, 85(20), 2000, pp. 4313-4316
We have studied the behavior of elastic constants A, B, and C deduced from
ultrasound velocity anisotropies in the vicinity of the nematic-smectic-A t
ransition of terephthal-bis-p-p'-butylaniline. A is associated with compres
sibility, B with layer compression, and C with the coupling between compres
sibility and layer compression. We show that the exponent of A is of the pr
easymptotic 3D-XY type, whereas those of B and C are in between the SD-XY v
alues and those associated with the anisotropic fixed point. This behavior
is consistent with the extended crossover regime predicted by Patton and An
dereck [Phys. Rev. Lett. 69, 1556 (1922)].