Evidence for intra-unit-cell magnetic order in Bi2Sr2CaCu2O8+δ

Polarized elastic neutron scattering measurements have been performed in the bilayer copper oxide system ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$, providing evidence for an intra-unit-cell magnetic order inside the pseudogap state. That shows time reversal symmetry breaking in that state as already reported in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ through dichroism in circularly polarized photoemission experiments. The magnetic order displays the same characteristic features as the one previously reported for monolayer ${\mathrm{HgBa}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ and bilayer ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+\mathit{x}}$, demonstrating that this genuine phase is ubiquitous of the pseudogap of high temperature copper oxide materials.