Universality of the q=1/2 Orbital Magnetism in the Pseudogap Phase of the High-T_c superconductor YBa_2Cu_3O_6+x

Several decades of debate have centered around the nature of the enigmatic pseudo-gap state in high temperature superconducting copper oxides. Recently, we reported polarized neutron diffraction measurements that suggested the existence of a magnetic texture bound to the pseudo-gap phase [Bounoua, et al. Communications Physics 5, 268 (2022)]. Such a magnetic texture is likely to involve the spontaneous appearance of loop currents within the CuO_2 unit cells, which give birth to complex correlated patterns. In the underdoped YBa_2Cu_3O_6.6, the magnetic structure factor of such an orbital magnetic texture gives rise to two distinct magnetic responses at q=0 and q=1/2. As this pattern alters the lattice translation invariance, such a state of matter could contribute to an instability of the Fermi surface. Here, we report polarized neutron scattering measurements on a nearly optimally doped high quality single crystal of YBa_2Cu_3O_6.9 that exhibits the same q=1/2 magnetism and a weakly overdoped YBa_2Cu_3O_7 sample where this signal is no longer sizeable. The in-plane and out-of-plane magnetic neutron scattering intensities in YBa_2Cu_3O_6.9 (at q=1/2) and YBa_2Cu_3O_6.85 (at q=0), reported previously, display the same temperature dependent hallmarks. The magnitudes of both q=0 and q=1/2 magnetic signals further exhibit the same trends upon doping in YBa_2Cu_3O_6+x, confirming that they are likely intertwined.