Physical origin of the dynamical central peak in ferroelectric triglycine sulfate

The picosecond time-resolved spectroscopy is carried out to clarify the physical origin of the central peak that has been reported in uniaxial ferroelectric triglycine sulfate (NH₂CH₂COOH)₃·H₂SO₄ (TGS). An ultraslow relaxational mode with a relaxation time τ=5--8 μsec is reported as a real-time signal intensity $I(t)$ and is assigned to a thermal relaxational mode. This assignment is based on the fact that the diffusion constant evaluated from τ agrees well with the thermal diffusivity measured by heat-pulse method. The discovered mode, the thermal relaxational mode, is proved to be the physical origin of the reported central peak of TGS from the anisotropic anomalous behavior of the signal intensity at time origin $I(0).$