Quasicritical heat capacity at a smectic-A–hexatic-Bphase transition

H. Haga, Z. Kutnjak, G. S. Iannacchione, S. Qian, D. Finotello, C. W. Garland
1997 Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics  
High-resolution ac calorimetry has been used to characterize the excess heat capacity ⌬C p (T) associated with the smectic-A (SmA) -hexatic-B (HexB) transition in n-hexyl-4Ј-n-pentyloxybiphenyl-4-carboxylate ͑65OBC͒. For temperature oscillations in the investigated frequency range 1.42-400 mHz, the ⌬C p data reveal no frequency dependence and correspond to static thermodynamic values. The present data resolve several discrepancies in previously reported C p values. This transition is very
more » ... ition is very weakly first order, but power-law fits could be made to ⌬C p . Such fits yield an effective critical exponent ␣ eff ϭ0.65Ϯ0.05, which agrees quite well with values of ϳ0.6 reported by Huang and co-workers ͓Phys. Rev. Lett. 46, 1289 ͑1981͒; Phys. Rev. A 28, 2433 ͑1983͒; Phys. Rev. Lett. 56, 1712 ͑1986͔͒. Such an exponent value disagrees strongly with the theoretically predicted three-dimensional XY value ␣ XY ϭϪ0.007. It is proposed that this C p behavior and also the reported order parameter variation, which yields an effective critical exponent ␤ eff of ϳ0.2, are consistent with quasitricritical or quasitetracritical ͑strain-smeared, very weak first-order͒ behavior arising from a coupling between the amplitude of the bond-orientational order and the in-plane positional strain.
doi:10.1103/physreve.56.1808 fatcat:2qmajscn2rerdb2wvln4vkm4qm