Abstract
Spin liquid (SL) systems have been the subject of much attention recently, as they have been theoretically predicted to not freeze, even at 0 K. Despite extensive searches being made for such a system, only a few candidates have been found. All of these candidates share geometrical frustrations that are based on triangular lattices. We applied vibrational spectroscopy to one of the candidates of a molecule-based SL system, and we compared its results against three antiferromagnetic compounds and four charge-ordered compounds. All of their structural motifs belong to triangular lattices. The C=C stretching modes in the SL state indicated that there were charge and lattice fluctuations. These fluctuations were suppressed but non-negligible in the AF compounds. This finding is potentially significant, as it indicates that a hidden lattice and charge fluctuation are the driving force of a geometrical frustration, which eventually leads to a SL state.
Highlights
It has been more than 40 years since Anderson predicted quantum spin liquid (SL) states using his resonating– valence bond model[1]
We have examined the inter-dimer bond alternation, intra-dimer bond alternation and inhomogeneous molecular charges of Sb-salt 2, which we believe to be a quantum SL
The vibrational spectroscopies that focused on the C=C stretching modes revealed that the dynamical fluctuation was due to the competition among the dimers, tetramers and octamers in the SL state
Summary
It has been more than 40 years since Anderson predicted quantum spin liquid (SL) states using his resonating– valence bond model[1]. Efforts have been made to discover an actual example of a quantum SL state in triangular, Kagomé and pyrochlore lattices[2] All of these lattice types are based on a triangular arrangement of the spin sites, which makes them incompatible with antiferromagnetic ordering. The results of magnetic and transport property measurements have revealed the absence of any ordering, even at low temperature, which suggests that a spin liquid (SL) state occurs in β′-EtMe3Sb[Pd(dmit)2]2, κ-(ET)2M2(CN)[3] and κ-H3(Cat-EDT-TTF)[214–23]. An additional important difference between them is that the inter- and intra-dimer transfer integrals are significantly smaller and larger, respectively, in X[Pd(dmit)2]2 than in κ-type compounds[24]. There are two kinds of VBO in X[Pd(dmit)2]2: the lattice distortions exhibiting the alternations in the inter- and intra-dimer transfer integrals. Using information from infrared (IR) and Raman spectra of P-salt 1, P-salt 2, Sb-salt 1 and Sb-salt 2, we report that the absence of any ordering and a small entropy releasing of a Sb-salt 2 can be ascribed to dynamical fluctuations due to the competition between different types of CO states that are accompanied by different types of VBOs
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