Proton Dynamics in the Anti-ferroelectric CsH$_{3}$(SeO$_{3})_{2}$ by using $^{1}$H NMR Measurements

$^{1}$H NMR techniques have been employed on the anti-ferroelectric CsH$_{3}$(SeO$_{3})_{2}$ to measure spectrum, shift, T$_{1}$ and T$_{2}$ from 300 K down to 80 K at 4.85 T. The $^{1}$H NMR spectrum at 300 K shows a composite structure; one dominant broad peak and two small narrow peaks. From the temperature dependences of both intensity and T$_{1}$ for each peak, we identify that the narrow peaks come from rapidly moving protons whereas the broad peaks originate from rigid protons. The spectra below 200 K show several peaks associated with six nonequivalent proton sites and also the T$_{1}$ decays show a non-exponential curve coming from many proton sites. T$_{1}$ is very long even at 300 K and becomes even longer at low temperature. By analyzing T$_{1}$ decays with T$_{1S}$ and T$_{1L}$, we confirm that 1/T$_{1}$(T) show an activated behavior; the short component originates from proton dynamics with activation energy of $\sim$ 140 K and the long component is associated with that of $\sim$ 100 K. Further analysis suggests that some protons show an abrupt change in both shift and T$_{1L}$ across T$_{c}$ and may be responsible for the phase transition.