Mechanisms of the antiferro-electric ordering in superprotonic conductors Cs3H(SeO4)2 and Cs3D(SeO4)2

Wide ranges of absorbance spectra were measured to elucidate a difference in the antiferro-electric (AF) ordering mechanisms below 50 and 168 K in Cs3H(SeO4)(2) and Cs3D(SeO4)(2), respectively. Collective excitations due to deuterons successfully observed at 610 cm(-1) exhibit a remarkable isotope effect. This indicates that the transfer state in the dimer of Cs3D(SeO4)(2) is dominated by a deuteron hopping in contrast to Cs3H(SeO4)(2), where a proton hopping makes a tiny contribution compared to a phonon-assisted proton tunneling (PAPT) associated with 440-cm(-1) def(bend) . The fluctuation relevant to the AF ordering in Cs3D(SeO4)(2) is not driven by the conventional deuteron hopping but by the phonon-assisted deuteron hopping associated with 310-cm(-1) def(bend) . Consequently, Cs3D(SeO4)(2) has a distinct ordering mechanism from Cs3H(SeO4)(2), in which quantum fluctuations toward the AF ordering are enhanced through the PAPT associated with the in-phase libration. Published under an exclusive license by AIP Publishing.

Automated summary

The difference in antiferro-electric ordering mechanisms below 50 and 168 K in Cs3H(SeO4)(2) and Cs3D(SeO4)(2) respectively was elucidated through measuring wide ranges of absorbance spectra. The presence of deuterons at 610 cm(-1) exhibited a significant isotope effect, indicating different dominations of deuteron and proton hopping in Cs3D(SeO4)(2) and Cs3H(SeO4)(2) respectively. The distinct ordering mechanism in Cs3D(SeO4)(2) is enhanced by the phonon-assisted deuteron hopping associated with 310 cm(-1) def(bend).