PRECURSOR OF A STRONG 1ST-ORDER PHASE-TRANSITION - CRITICAL SPEEDING-UP OF FLUORESCENCE LIFETIME IN THE ALPHA-BETA-TRANSITION OF RESORCINOL

A precursor of a strong first-order structural phase transition has be en detected as the critical speeding-up of the lifetime of the fluores cence excited by a picosecond pulsed laser. In the alpha-beta transiti on of a resorcinol (C6H4(OH)2) crystal, a critical decrease of the lif etimes and an increase in the intensity of the impurity-induced fluore scence were found from about 30 K below T(c). This is in contrast with the fact that the temperature dependence of the Raman spectra and the dielectric constant shows no precursor effect. From a detailed polari zation study, large-amplitude and short-lived vibrational fluctuations associated with the phase transition are suggested as a possible orig in of the precursor. Despite the apparent contradiction of the fluctua tion-dissipation theorem, the results indicate that divergence of the fluctuation also takes place in the first-order phase transition. The method provides a new approach to the study of a first-order phase tra nsition.