期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：14
DOI：10.1073/pnas.2118492119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Chirality, the property of an object that cannot be superimposed on its mirror image, plays an essential role in condensed matter, such as magnetic, electronic, and liquid crystal systems. Topological phases emerge in such chiral materials, wherein helical and vortex-like structures—called skyrmions—are observed. However, the role of elastic fields in these topological phases remains unexplored. Here, we construct a molecular model of two-dimensional crystals incorporating steric anisotropy and chiral interactions to elucidate this problem. The coupling between the elastic fields and phase transitions between uniform, helical, and half-skyrmion phases can be utilized to switch these topological phases by external forces. Our results provide a fundamental physical principle for designing topological materials using chiral molecular and colloidal crystals.
Topological phase transitions into skyrmion and half-skyrmion (meron) phases are widely observed in condensed matter, such as chiral magnets and liquid crystals. They are utilized to design magnetoelectric, optical, and mechanoresponsive materials by controlling such topological phases. However, the role of the elastic field in nonuniform topological phases is elusive, though the essential role of crystal elasticity in uniform ordered crystal phase has been recognized. To elucidate this problem, we construct a model describing chiral molecules and colloids in quasi-two-dimensional molecular crystals, which incorporates intermolecular chiral twisting and spheroidal steric interactions. We reveal that emergence of the elastic fields from the competition between steric anisotropy and intermolecular twisting is a key to control uniform, helical, and half-skyrmion structures. By utilizing the coupling between the spheroidal orientations and the elastic fields, these topological phases are switched by temperature, external electromagnetic fields, and anisotropic stresses, where a re-entrant phase transition between the helical and the half-skyrmion phases is discovered. Our results imply that controlling the emergent elastic fields is crucial for obtaining a fundamental physical principle for controlling topological phases using chiral molecular and colloidal crystals.
