The mineral malachite, Cu2(OD)2CO3, has a quantum spin-liquid ground state and no long-range magnetic order down to at least T=0.4 K. Inelastic neutron scattering measurements show that the excitation spectrum consists of dispersive gapped singlet-triplet excitations, characteristic of spin-1/2 dimer-forming Heisenberg antiferromagnets. We identify a new two-dimensional dimerized coupling scheme with strong interdimer coupling J'/J1~0.3 that places malachite between strongly coupled alternating chains, square lattice antiferromagnets, and infinite-legged ladders. The geometry of the interaction scheme resembles the staggered dimer lattice, which may allow unconventional quantum criticality.
@article{arxiv.1412.5908,
title = {Spin excitations in the two-dimensional strongly coupled dimer system malachite},
author = {E. Canevet and B. Fak and R. K. Kremer and J. H. Chun and M. Enderle and E. E. Gordon and J. L. Bettis and M. -H. Whangbo and J. W. Taylor and D. T. Adroja},
journal= {arXiv preprint arXiv:1412.5908},
year = {2015}
}