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Letter

Nature Physics 3, 96–99 (1 February 2007) | doi:10.1038/nphys522

Gapped itinerant spin excitations account for missing entropy in the hidden-order state of URu2Si2

C. R. Wiebe , J. A. Janik , G. J. MacDougall , G. M. Luke , J. D. Garrett , H. D. Zhou , Y.-J. Jo , L. Balicas , Y. Qiu , J. R. D. Copley , Z. Yamani & W. J. L. Buyers

Many correlated electron materials, such as high-temperature superconductors, geometrically frustrated oxides and low-dimensional magnets, are still objects of fruitful study because of the unique properties that arise owing to poorly understood many-body effects. Heavy-fermion metals—materials that have high effective electron masses due to those effects—represent a class of materials with exotic properties, ranging from unusual magnetism, unconventional superconductivity and |[lsquo]|hidden|[rsquo]| order parameters.