Magnetic state of Barlowite 2 elucidated by magnetic neutron diffraction on a single crystal. All occupancy values are taken from SCXRD at NSF’s ChemMatCARS.

npj: Quantum Material, 5, 23 (2020)

DOI: 10.1038/s41535-020-0222-8

Newly synthesized crystalline barlowite (Cu4(OH)6FBr) and Zn-substituted barlowite demonstrate the delicate interplay between singlet states and spin order on the spin-1212 kagome lattice. Comprehensive structural measurements demonstrate that our new variant of barlowite maintains hexagonal symmetry at low temperatures with an arrangement of distorted and undistorted kagome triangles, for which numerical simulations predict a pinwheel valence bond crystal (VBC) state instead of a QSL. The presence of interlayer spins eventually leads to an interesting pinwheel q = 0 magnetic order. Partially Zn-substituted barlowite (Cu3.44Zn0.56(OH)6FBr) has an ideal kagome lattice and shows QSL behavior, indicating a surprising robustness of the QSL against interlayer impurities. The magnetic susceptibility is similar to that of herbertsmithite, even though the Cu2+ impurities are above the percolation threshold for the interlayer lattice and they couple more strongly to the nearest kagome moment. This system is a unique playground displaying QSL, VBC, and spin order, furthering our understanding of these highly competitive quantum states.

Rebecca W. Smaha 1,2,12, Wei He 1,3,12, Jack Mingde Jiang 1,4, Jiajia Wen 1, Yi-Fan Jiang 1, John P. Sheckelton 1, Charles J. Titus 5, Suyin Grass Wang 6, Yu-Sheng Chen 6, Simon J. Teat 7, Adam A. Aczel 8,9, Yang Zhao 10,11, Guangyong Xu10, Jeffrey W. Lynn 10, Hong-Chen Jiang 1 and Young S. Lee 1,4

1 Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.

2 Department of Chemistry, Stanford University, Stanford, CA 94305, USA.

3 Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA.

4 Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.

5 Department of Physics, Stanford University, Stanford, CA 94305, USA.

6 NSF’s ChemMatCARS, Center for Advanced Radiation Sources, c/o Advanced Photon Source/ANL, The University of Chicago, Argonne, IL 60439, USA.

7 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

8 Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.

9 Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA.

10 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899-6102, USA.

11 Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA.

12 These authors contributed equally.