Gapless quantum spin liquid in the S = 1/2 anisotropic kagome antiferromagnet ZnCu₃(OH)₆SO₄

Abstract

We have successfully synthesized the new S = 1/2 anisotropic kagome antiferromagnet ZnCu 3 (OH) 6 SO 4 and determined its structure by synchrotron x-ray diffraction. No magnetic ordering is observed down to 50 mK, despite a moderately high Weiss temperature of Θ w ∼ −79 K, indicating that the compound is a new quantum spin liquid (QSL) candidate. A linear temperature dependence of the magnetic heat capacity is found at 6 ∼ 15 K and below 0.6 K. Temperatureindependent intrinsic susceptibilities are observed exactly in both temperature ranges. This consistently suggests a gapless QSL below 0.6 K, which may evolve from an unconventional quantum spin state at higher temperatures (6 ∼ 15 K).

Barlowite as a canted antiferromagnet: Theory and experiment

“…The paratacamite family of compounds has proven to be a fertile ground for kagome materials with different properties. The Zn x Cu 4−x (OD) 6 Cl 2 series of materials has been found to form valence-bond solids due to distortions of the kagome layer in monoclinic space groups 4 . The replacement of Zn 2+ in ZnCu 3 (OH) 6 Cl 2 by a nonmagnetic ion like Mg 2+ possibly leads to another spin-liquid candidate 5 , as does replacement of 2Cl − by SO 2− 4 6 .…”

“…The Zn x Cu 4−x (OD) 6 Cl 2 series of materials has been found to form valence-bond solids due to distortions of the kagome layer in monoclinic space groups 4 . The replacement of Zn 2+ in ZnCu 3 (OH) 6 Cl 2 by a nonmagnetic ion like Mg 2+ possibly leads to another spin-liquid candidate 5 , as does replacement of 2Cl − by SO 2− 4 6 . On the other hand, magnetic ions between the kagome layers lead to compounds that order magneti- 6 FBr as a layered structure of two-dimensional Cu-based perfect kagome planes and reported the observation of antiferromagnetic order at low temperatures based on thermodynamic measurements on polycrystalline samples.…”

“…The replacement of Zn 2+ in ZnCu 3 (OH) 6 Cl 2 by a nonmagnetic ion like Mg 2+ possibly leads to another spin-liquid candidate 5 , as does replacement of 2Cl − by SO 2− 4 6 . On the other hand, magnetic ions between the kagome layers lead to compounds that order magneti- 6 FBr as a layered structure of two-dimensional Cu-based perfect kagome planes and reported the observation of antiferromagnetic order at low temperatures based on thermodynamic measurements on polycrystalline samples. In the present work we go beyond previous studies and suggest a novel synthetic route to successfully obtain perfect kagome structures, exemplarily realized in the mineral barlowite.…”

“…1 (c)). Following this recipe via the chemical synthesis of Cu 4 (OH) 6 FBr, we arrive at perfectly aligned kagome planes as shown in Fig. 1 (d).…”

“…This compound is known as the mineral barlowite 15 . Single crystals of barlowite, Cu 4 (OH) 6 FBr, were grown synthetically through the hydrothermal reaction of copper carbonate basic (malachite), with perbromic acid in the presence of ammonium fluoride. The crystal structure of Cu 4 (OH) 6 FBr was determined by single crystal X-ray diffraction measurements 17 at ambient temperature and is shown in Fig.…”