Analysis of the Raman frequencies close to the λ-phase transition in NH4Cl

Our β value is very close to zero for all the modes studied in NH4Cl close to its λ-phase transition. This indicates that the soft mode-hard mode coupling theory predicts a logarithmic divergence of the Raman frequencies of those modes considered here, as the temperature increases toward the λ transition temperature Tλ in NH4Cl.