Origin of theT32specific-heat term in triglycine sulfate at low temperatures

Two sets of specific-heat experiments on single crystals of ferroelectric triglycine sulfate (TGS) at low temperatures are reported aimed at discriminating between bulk and surface contributions to the unusual $T^{\frac{3}{2}}$ specific-heat term. In the first set, two large crystals with small surface-to-volume ratios ($\frac{S}{V}$) were measured, where one (poled) crystal was single domain and the other crystal multidomain. In the second set, two assemblies of small TGS crystals with large $\frac{S}{V}$ values were measured. The data demonstrate that a surface excitation is responsible for the $T^{\frac{3}{2}}$ term in TGS, and an unusually thick ($\simeq 0.02$ cm) surface layer is indicated.