Nature, 455, 372 (2008)Y. Li, V. Balédent, N. Barišić, Y. Cho, B. Fauqué, Y. Sidis, G. Yu, X. Zhao, P. Bourges, and M. Greven

Unusual magnetic order in the pseudogap region of the superconductor HgBa₂CuO_4+δ