Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu₃Zn(OH)₆FBr

Abstract

We report a new kagome quantum spin liquid candidate Cu3Zn(OH)6FBr, which does not experience any phase transition down to 50 mK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature (∼ 200 K). A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from 19 F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fractionalization in the fractional quantum Hall state.

Materializing rival ground states in the barlowite family of kagome magnets: quantum spin liquid, spin ordered, and valence bond crystal states

“…(33) Polycrystalline samples show no magnetic order, and a gapped ground state with Z 2 topological order has been proposed. (31,35,36) The first single crystals of Znsubstituted barlowite were recently synthesized with x = 0.33, which suppresses magnetic order to T = 4 K. (30) Our novel synthesis techniques produce large single crystals of barlowite and Zn-substituted barlowite, and measurements of the magnetic and structural properties allow for detailed studies of how the QSL tendencies on the S = 1 2 kagome lattice are affected by subtle structural symmetry-lowering and magnetic impurities on the interlayer sites.…”

Gapless ground state in the archetypal quantum kagome antiferromagnet ZnCu3(OH)6Cl2

“…Our NMR spectra at high-T were obtained by varying the frequency through all the transitions, then recombining the various Fourier transforms. Below 100 K, our spectra were obtained using field sweeps at a given frequency for typical frequencies 39.054; 25.013; 15.338 MHz used in most cases, corresponding to reference fields of 6.766; 4.334; 2.657 T.…”

“…It is recognized as the kagome spin liquid candidate approaching so far the best the ideal model of an Heisenberg AntiFerromagnetic Hamiltonian on the Kagome lattice (KHAF) [13], now available in single crystal form. Its discovery triggered a burst of experimental activity, on one hand with the materials search for Cu 2+ -based S = 1/2 variants obtained either from a change of anions [14][15][16] or replacement of Zn 2+ cations [17][18][19][20] and Li + intercalation in view of charge doping [21], and on the other hand with V 4+ -based S = 1/2 [22,23] QSL candidates.…”

Coexistence of magnetic order and persistent spin dynamics in a quantum kagome antiferromagnet with no intersite mixing

“…This is substantial in the paradigmatic herbertsmithite compound, ZnCu 3 (OH) 6 Cl 2 , where the Cu-Zn intersite mixing amounts to 5-10% [19]. Other QKA spinliquid candidates, like tondiite MgCu 3 (OH) 6 Cl 2 [20], Zn-brochantite ZnCu 3 (OH) 6 SO 4 [21], and Zn-barlowite ZnCu 3 (OH) 6 FBr [22] suffer from a very similar amount of magnetic/non-magnetic ion mixing. Such mixing can in principle be reduced by introducing larger non-magnetic ions, like in the cases of CaCu 3 (OH) 6 Cl 2 · 0.7H 2 O [23] and EuCu 3 (OH) 6 Cl 3 [24], which however both order magnetically.…”