Controlled Frustration Release 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 controlled tuning of the frustration strength, separating its effects from those of disorder and other factors, is pending. Here, we perform comprehensive 1H NMR measurements on Y3Cu9(OH)(19)Cl-8 single crystals revealing an unusual (Q) over right arrow = (1/ 3 x 1/3) antiferromagnetic state below T-N = 2.2 K. By applying in situ uniaxial stress, we break the symmetry of this disorder-free, frustrated kagome system in a controlled manner yielding a linear increase of T-N with strain, in line with theoretical predictions for a distorted kagome lattice. In-plane strain of approximate to 1% triggers a sizable enhancement Delta T-N/T-N approximate to 10% due to a release of frustration, demonstrating its pivotal role for magnetic order.