Search for the existence of circulating currents in high-$T_c$   superconductors using the polarized neutron scattering technique
  We review experimental attempts using polarized neutron scattering technique to reveal the existence in high temperature superconductors of a long-range ordered state characterized by the spontaneous appearance of current loops. We draw a particular attention to our recent results (B. Fauqu\'e {\it et al.}, {\it Phys. Rev. Lett.} {\bf 96}, 197001 (2006)) that, up to now, can be explained only by the theory of circulating current proposed by C.M. Varma. 
Yvan Sidis, Benoit Fauqu\'e, Vivek Aji and Philippe Bourges