新物質<i>A</i>（TiO）Cu<sub>4</sub>（PO<sub>4</sub>）<sub>4</sub>（<i>A</i>＝Ba, Sr）における結晶カイラリティの強度とドメイン構造の相関

Abstract

Crystal chirality, a label defining the handedness of a system without improper symmetry, has long been an intensive subject in a variety of research fields such as chemistry, biology, and solid-state physics. Its great importance in solid-state physics lies in the potential unique functionalities of chiral materials such as optical activity, piezoelectricity, and recently discovered unconventional magnetism and associated magneto-transport and magnetoelectric phenomena. An important step toward further development of the chirality research would be a quantification of chirality and a clarification of its relationship to physical properties. Here, we report the discovery of two novel chiral materials, A(TiO)Cu4(PO4)4 (A＝Ba, Sr), and the detailed characterization of their crystal and chiral domain structures. We identify that the chiral crystal structure of this system can be characterized by an antiferrorotative distortion of structural units, indicating that the rotation angle is a good quantitative measure of the chirality strength. Interestingly, the rotation angle and thus the chirality strength can be tuned by changing A site cations. We observe striking differences in the occurrence frequency of chiral domains in the two materials：weakly chiral Ba(TiO)Cu4(PO4)4 mostly hosts a multidomain state, while strongly chiral Sr(TiO)Cu4(PO4)4 predominantly shows monodomain state. On the basis of these results, we discuss the relationship between the chirality strength and the occurrence frequency of chiral domains in this system.