Recent Advances in Quantum Spin Liquids in Two-Dimensional Kagome System YCu₃(OH)_6+xX_3-x (X = Cl, Br)

The two-dimensional kagome lattice serves as a prototypical platform for exploring quantum spin liquids owing to its pronounced geometric frustration. Substantial advancements have been achieved in herbertsmithite and its structural analogs. These quantum spin liquid candidates exhibit large superexchange interactions yet resist magnetic ordering down to the lowest measurable temperatures, which are typically three or four orders of magnitude below the energy scale of the primary exchange energies. Nevertheless, the existence of unavoidable intrinsic interlayer magnetic impurities leads to persistent debates on their ground states. A breakthrough emerged with the discovery of YCu₃(OH)_6+xX_3-x (X = Cl, Br), a novel material family rigorously verified to eliminate magnetic impurity interference. This short review highlights critical advances in these materials, emphasizing experimental signatures consistent with a Dirac quantum spin liquid and the observation of a oneninth magnetization plateau and possible quantum oscillations. Local structural characteristics play a crucial role in clarifying the complex emergent quantum phenomena of these materials. Collectively, these findings establish this material class as a promising platform for investigating quantum spin liquid behavior in two-dimensional kagome lattices.