Possible spin gap in a clean sample of the quantum spin liquid candidate: herbertsmithite

The mineral herbertsmithite (HS), ZnCu3(OD)6Cl2, is a prominent candidate to display a quantum spin liquid (QSL) phase. The Cu(2+) spins (s=1/2) in HS are arranged in a 2D kagome lattice and couple antiferromagnetically. The material has been found to not order down to 50 mK, even though the Curie-Weiss temperature is around -300 K. However, HS is prone to structural disorder between Zn and Cu, disrupting the kagome symmetry and introducing coupling between layers. For this reason, experimental results have been interpreted with caution. We have utilized solid state NMR to quantify the structural disorder that is almost invisible by diffraction methods. The samples with the lowest disorder signal display a clear peak in AC-susceptibility at 200 mK, suggesting either magnetic order or the opening of a spin gap of the order 20 micro-eV. Therefore, we believe it is timely to revisit the question of magnetic order and fluctuations in HS. We aim to study our powder sample using OSIRIS, high-resolution spectroscopy data.