STRONG CRITICAL FLUCTUATIONS NEAR A STRONGLY FIRST-ORDER SMECTIC-C-HEXATIC-F PHASE-TRANSITION

We present the first experimental evidence of strong anomalies in both the attenuation and velocity of longitudinal ultrasound near a smecti c-C-hexatic-F phase transition, These effects, which have been observe d on terephthal-bis-hexylaniline, show that the hexatic order paramete r is strongly coupled to density. They occur although the transition i s strongly first order, with a wide two-phase region of similar to 3 d egrees C, Analysis of the data enables the specific-heat exponent to b e determined, The results also show that the transition occurs in a hi ghly fluctuating layer system.