The kagome Heisenberg antiferromagnet formed by frustrated spins arranged in a lattice of corner-sharing triangles is a prime candidate for hosting a quantum spin liquid (QSL) ground state consisting of entangled spin singlets¹. However, the existence of various competing states makes a convincing theoretical prediction of the QSL ground state difficult², calling for experimental clues from model materials. The kagome lattice materials Zn-barlowite (ZnCu₃(OD)₆FBr)^3,4,5 and herbertsmithite (ZnCu₃(OD)₆Cl₂)^6,7,8,9,10 do not exhibit long-range order and are considered the best realizations of the kagome Heisenberg antiferromagnet known so far. Here we use ⁶³Cu nuclear quadrupole resonance combined with the inverse Laplace transform^11,12,13 to locally probe the inhomogeneity of delicate quantum ground states affected by disorder^14,15,16,17. We present direct evidence for the gradual emergence of spin singlets with spatially varying excitation gaps, but even at temperatures far below the super-exchange energy scale their fraction is limited to ~60% of the total spins. Theoretical models^18,19 need to incorporate the role of disorder to account for the observed inhomogeneously gapped behaviour.

^{由排列在角共享三角形晶格中的受挫自旋形成的 Kagome Heisenberg 反铁磁体是承载由纠缠自旋单重态1}组成的量子自旋液体 (QSL) 基态的主要候选者。然而，各种竞争状态的存在使得对 QSL 基态的令人信服的理论预测变得困难²，需要从模型材料中获得实验线索。Kagome 晶格材料 Zn-barlowite (ZnCu ₃ (OD) ₆ FBr) ^3,4,5和 Herbertsmithite (ZnCu ₃ (OD) ₆ Cl ₂ ) ^6,7,8,9,10不表现出长程有序，被认为是迄今为止已知的kagome海森堡反铁磁体的最佳实现。在这里，我们使用⁶³ Cu 核四极共振结合逆拉普拉斯变换^11,12,13来局部探测受无序影响的微妙量子基态的不均匀性^14,15,16,17。我们提供了具有空间变化激发间隙的自旋单线态逐渐出现的直接证据，但即使在远低于超交换能标的温度下，它们的比例也仅限于总自旋的约 60%。理论模型^18,19需要结合无序的作用来解释观察到的不均匀间隙行为。