Initiative Highlight
A new spin on matter
For years, theorists have predicted the possibility of new states of matter including a peculiar state of a spin-1/2 kagomé lattice called the “quantum spin liquid.” The spin liquid state differs from conventional phases in that the spins associated with electrons can take on unique ordered arrangements. Despite heavy theoretical interest, experimental studies of the spin-1/2 kagomé lattice have been hampered by the difficulty in synthesizing such materials. Recently, Nocera and Lee of the MIT MRSEC have synthesized and studied such a system called herbertsmithite with chemical formula ZnCu3(OH)6Cl2 (J.S. Helton et al., Phys. Rev. Lett. 98, 107204 (2007)). As shown in the Figure, the structure of herbertsmithite is composed of S=1/2 Cu ions forming kagomé layers separated by non-magnetic Zn layers. Results suggest that an unusual spin-liquid state with essentially gapless excitations is realized in this material. In a recent breakthrough, a hydrothermal method that yields appreciably sized single crystalline samples (see Figure) has been developed, and crystals as large as 2 mm have been grown. This discovery was covered by the press in the February 2007 issue of Physics Today: “New candidate emerges for a quantum spin liquid” (http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_60/iss_2/16_1.shtml). The availability of such crystals will enable rapid progress in unraveling the mysteries of these unusual states of matter.
Left: Crystal structure of the S=1/2 kagome lattice material herbertsmithite.
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