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Kagomé antiferromagnets present an ideal construct for studying the unusual physics that result from the placement of magnetically frustrated spins on a low-dimensional lattice. While any two nearest-neighbor spins within the corner-sharing equilateral triangles of the kagomé lattice can couple antiferromagnetically, the third cannot - it is frustrated.
Much interest in preparing model spin-frustrated systems is driven by the potential of such compounds to explain conduction mechanisms in high-Tc superconductors. Nearly two decades ago, Anderson proposed that the resonating valence bond (RVB) state may explain the scatterless hole transport in doped rare-earth cuprates. The quantum spin liquid phase responsible for RVB is most likely to be found in low-dimensional, low-spin, geometrically frustrated systems. Most theoretical investigations of RVB have focused on S = ½ antiferromagnets on kagomé lattices due to their higher degree of geometric frustration relative to triangular lattices. However, a lack of pure kagomé based materials (and most especially those of S = ½) has long prevented incisive measurement of their magnetic properties and experimental testing of RVB theory on real spin-frustrated kagomé systems. We have recently prepared the first pure S = ½ kagomé lattices. Neutron scattering measurements show that the new kagomé lattice does not magnetically order down to 50 milli-Kelvin, suggesting the realization of a new state of matter - the quantum spin liquid. Investigation of these unprecedented materials is performed in collaboration with the Lee group in the MIT Department of Physics.