Pinwheel valence-bond solid and triplet excitations in the two-dimensional deformed kagome lattice

Determining ground states of correlated electron systems is fundamental to understanding unusual phenomena in condensed-matter physics. A difficulty, however, arises in a geometrically frustrated system in which the incompatibility between the global topology of an underlying lattice and local spin interactions gives rise to macroscopically degenerate ground states ¹ , potentially prompting the emergence of quantum spin states, such as resonating valence bond ^2-7 and valence-bond solid ^8-11 (VBS). Although theoretically proposed to exist in a kagome lattice-one of the most highly frustrated lattices in two dimensions being comprised of corner-sharing triangles-such quantum-fluctuation-induced states have not been observed experimentally. Here we report the first realization of the 'pinwheel' VBS ground state in the S=1/2 deformed kagome lattice antiferromagnet Rb ₂ Cu ₃ SnF ₁₂ (refs 12, 13). In this system, a lattice distortion breaks the translational symmetry of the ideal kagome lattice and stabilizes the VBS state.