Field-induced spin-density wave beyond hidden order in URu2Si2
  URu2Si2 is one of the most enigmatic strongly-correlated-electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically-ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to an instrumentation breakthrough in high-field neutron scattering, we identify the field-induced phases of URu2Si2 as a spin-density-wave state with wavevector k1 = (0.6 0 0). The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations, and the Fermi surface is emphasized, calling for dedicated band structure calculations. 
W. Knafo, F. Duc, F. Bourdarot, K. Kuwahara, H. Nojiri, D. Aoki, J.   Billette, P. Frings, X. Tonon, E. Leli\`evre-Berna, J....
cond-mat.str-el