Quantum spin liquid (QSL) is a theoretical model of spins with antiferromagnetic interactions. These spins fluctuate down to the absolute zero temperature without any long-range magnetic order but exhibit quantum entanglement [1]. A key aspect for realization of such theoretical concept is a geometrical frustration of these spins. In theory various QSL states have been identified, but much harder is to find a material, where this concept can be tested. Today only few materials are considered as QSL candidates. One of them is the mineral herbertsmithite, ZnCu3(OH)6Cl2 [2]. The Cu2+ (S = 1/2) ions in this compound form a quasi-2D layered structure with kagome lattice [3]. Such a lattice exhibits high degree of frustration which is ideal for QSL. The rhombohedral crystal lattice (ideal kagome lattice) is stabilized by the Zn ions. The mineral clinoatacamite without Zn ions, Cu4(OH)6Cl2, is then monoclinic and consequently antiferromagnetic order is stabilized at low temperatures [4]. The investigation of the ground state properties in the Zn-substituted series, ZnxCu4-x(OH)6Cl2, has therefore motivated numerous studies over the past two decades, usually on powder samples. In addition to their intriguing magnetic properties these compounds are also interesting from structural point of view. It is demonstrated by high amount of structural polymorphs. The presented study of single-crystalline samples is focused on the relation among these polymorphs and their ground-state properties, studied by low-temperature X-ray diffraction and specific heat measurements.
This work was supported by the Czech Science Foundation via research project GAČR 23-06810O.