Spin liquid properties of the kagome material Cu3(HOTP)2
Abstract
The metal-organic-framework (MOF) compound Cu3(HOTP)2, a.k.a. Cu3(HHTP)2, is a small-gap semiconductor containing a kagome lattice of antiferromagnetically coupled S=1/2 CuII spins with intra-layer nearest-neighbor exchange coupling J 2 K. The intra-layer J value obtained from DFT+U calculations is shown to match with the experimental value for reasonable values of U. Muon spin relaxation confirms no magnetic ordering down to 50~mK and sees spin fluctuations diffusing on a 2D lattice, consistent with a quantum spin liquid (QSL) ground state being present within highly decoupled kagome layers. Reduction of the spin diffusion rate on cooling from the paramagnetic region to the low-temperature QSL region reflects quantum entanglement. It is also found that the layers become more strongly decoupled in the low-temperature QSL region. Comparison of results for the spin diffusion, magnetic susceptibility and specific heat in the QSL region suggests close proximity to a quantum critical point and a large density of low energy spinless electronic excitations. A Z2-linear Dirac model for the spin excitations of the QSL is found to provide the best match with experiment.
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