Preasymptotic 3D XY Critical Behavior of Heat Capacity at Normal-Incommensurate Phase Transition in K_2ZnCl_4 and K_2SeO_4

Abstract

Heat capacity of K₂ZnCl₄ and K₂SeO₄ has beenmeasured using a high-resolution ac calorimeter. Critical behavior ofthe heat capacity anomalies associated with the normal-incommensurate(N-INC) phase transitions has been analyzed with the preasymptoticrenormalization-group expression which includes correction terms up tothe second order. It is revealed that the heat capacity anomalies ofK₂ZnCl₄ and K₂SeO₄ are described well with the threedimensional (3D) XY model; the critical exponent, the criticalamplitude ratio and the dimensionless ratio derived from thefirst-order correction terms agree well with the theoreticallyexpected values of 3D XY model. These results are consistent with ourprevious experimental result for Rb₂ZnCl₄ and the Cowley andBruce's prediction that the N-INC phase transition is classified intothe 3D XY system.