Abstract
Synthetic barlowite, Cu4(OH)6BrF, has emerged as a new quantum spin liquid (QSL) host, containing kagomé layers of S=1/2Cu2+ 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 F19 and H1 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)Å,b=11.521(2)Å,c=9.256(18)Å, 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 kagomé lattices even in the presence of small symmetry-breaking distortions. Thus, synthetic barlowite demonstrates universality of the physics of synthetic Cu2+ kagomé minerals and furthers the development of real QSL states.
| Original language | English |
|---|---|
| Article number | 044406 |
| Journal | Physical Review Materials |
| Volume | 2 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 27 2018 |
Funding
We acknowledge stimulating discussions with Collin Broholm. We thank Maxime Siegler for assistance with the single-crystal x-ray diffraction measurements, Craig Brown for assistance with the powder neutron diffraction measurements, and R. Campbell-Kelly at the Westinghouse Electric Company Columbia Fuel Fabrication Facility for performing ICP-MS measurements. Work at the Institute for Quantum Matter was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences and Engineering under Grant No. DEFG02-08ER46544. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. We acknowledge the support of the National Institute of Standards and Technology, U.S. Department of Commerce, in providing the powder neutron diffraction facilities used in this work. Certain commercial equipment, instruments, or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. T.M.M. acknowledges support of the David and Lucile Packard Foundation. I.H. and R.S. are supported by the Estonian Research Agency Grants No. IUT23-7 and No. PRG4, and the European Regional Development Fund Project No. TK134.