Controlling frustrated magnetism on the kagome lattice by uniaxial-strain tuning

It is predicted that strongly interacting spins on a frustrated lattice may lead to a quantum disordered ground state or even form a quantum spin liquid with exotic low-energy excitations. However, a thorough tuning of the frustration strength, separating its effects from those of disorder and other factors, is pending. Here we break the symmetry of a kagome-lattice compound in a controlled manner by applying $in$ $situ$ uniaxial stress. The transition temperature of ${\mathrm{Y}}_3\mathrm{C}{\mathrm{u}}_9(\mathrm{O}\mathrm{H}{)}_{18}\mathrm{O}\mathrm{C}{\mathrm{l}}_8$ is linearly enhanced with strain, $\mathrm{\Delta }{T}_{\mathrm{N}}\mathrm{/}{T}_{\mathrm{N}}\approx 10\mathrm{\%}$ upon in-plane compression of order $1\mathrm{\%}$, providing clear evidence for a release of frustration and its pivotal role for magnetic order. Our comprehensive ${}^1$H NMR results suggest a $\overrightarrow{Q}=(1\mathrm{/}3\times 1\mathrm{/}3)$ state under unstrained conditions and further reveal an incomplete antiferromagnetic transition with fluctuating moments in this strongly frustrated system.