Materials Science

Refusing to Order

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Science  22 Jun 2012:
Vol. 336, Issue 6088, pp. 1484
DOI: 10.1126/science.336.6088.1484-b

In magnetic materials, neighboring electron spins are aligned and point in either the same or opposite directions; the latter order is called antiferromagnetic. If the spins are arranged in, e.g., a triangular lattice, the antiferromagnetic condition cannot be satisfied everywhere simultaneously, and it is in principle possible for the system to remain disordered down to the lowest temperatures, giving rise to exotic ground states. However, other types of order or distortions usually intervene. Sheckelton et al. engineered the material LiZn2Mo3O8, where clusters of Mo3O13 are arranged in planes of triangular lattices. These clusters have an electron delocalized across the three Mo atoms, which makes the electronic structure stable against symmetry-breaking distortions; the clusters have an effective spin 1/2. Neutron diffraction and heat capacity measurements indicated that the material does not order magnetically down to 0.1 K and that at 96 K, two-thirds of the effective magnetic moments form singlets. Further experiments are needed to elucidate the nature of the ground state, but existing data suggest that the singlets are dynamic, forming an exotic condensed valence bond state, similar to the resonating valence bond state proposed to describe the high-temperature superconductivity of cuprates.

Nat. Mater. 11, 493 (2012).

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