Single crystal growth of Cu4(OH)6BrF and universal behavior in quantum spin liquid candidates synthetic barlowite and herbertsmithite

• Published in: arXiv.org
• Main Authors: Pasco, C M, Trump, B A, Tran, Thao T, Kelly, Z A, Hoffmann, C, Heinmaa, I, Stern, R, McQueen, T M
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 17.01.2018
• Subjects: Broken symmetry; Copper; Crystal growth; Diffraction; Electron diffraction; Interlayers; Lattice parameters; Lattices; Magnetic permeability; NMR spectroscopy; Physics - Materials Science; Physics - Strongly Correlated Electrons; Single crystals; Spectrum analysis; Spin liquid; Substitutes; Zinc
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1801.05769

Synthetic barlowite, Cu4(OH)6BrF, has emerged as a new quantum spin liquid (QSL) host, containing kagome layers of S=1/2 Cu2+ ions separated by interlayer Cu2+ ions. Similar to synthetic herbertsmithite, ZnCu3(OH)6Cl2, it has been reported that Zn2+ substitution for the interlayer Cu2+ induces a QSL ground state. Here we report a scalable synthesis of single crystals of Cu4(OH)6BrF. Through x-ray, neutron, and electron diffraction measurements coupled with magic angle spinning 19F and 1H NMR spectroscopy, we resolve the previously reported positional disorder of the interlayer Cu2+ ions and find that the structure is best described in the orthorhombic space group, Cmcm, with lattice parameters a = 6.665(13) A, b = 11.521(2) A, c = 9.256(18) A and an ordered arrangement of interlayer Cu2+ ions. Infrared spectroscopy measurements of the O-H and F-H stretching frequencies demonstrate that the orthorhombic symmetry persists upon substitution of Zn2+ for Cu2+. Specific heat and magnetic susceptibility measurements of Zn-substituted barlowite, ZnxCu4-x(OH)6BrF, reveal striking similarities with the behavior of ZnxCu4-x(OH)6Cl2. These parallels imply universal behavior of copper kagome lattices even in the presence of small symmetry breaking distortions. Thus synthetic barlowite demonstrates universality of the physics of synthetic Cu2+ kagome minerals and furthers the development of real QSL states.