Search for the existence of circulating currents in high-Tc 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 particular attention to our recent results (B. Fauqué et al., Phys. Rev. Lett. 96 (2006) 197001) that, up to now, can be explained only by the theory of circulating currents proposed by Varma.