Very-low-temperature pyroelectric response of a triglycine sulfate single crystal

Triglycine sulfate gives a low-temperature pyroelectric response which has been studied down to 0.4 K. This pyroelectricity exhibits two principal features: (i) The pyroelectric responsivity (i.e., ratio of pyroelectric coefficient to specific heat) shows a broad maximum at about 16 K, which can be explained by the influence of a low-lying mode at {~}46 cm^-1, in agreement with specific-heat and spontaneous-polarization measurements, and within the framework of previously developed models; (ii) for $T<1.9$ K, the pyroelectric responsivity, measured with a specially designed pumped liquid-³He cryostat, is significantly constant down to 0.4 K. It could thus be the first experimental verification of the statement of Born and of Szigeti about the pyroelectric behavior near $T=0$.