Universality of the {\bf q}=1/2 Orbital Magnetism in the Pseudogap Phase of the High-$T_c$ superconductor $\rm YBa_{2}Cu_{3}O_{6+x}$

Abstract

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, {\it 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 ${\rm YBa_{2}Cu_{3}O_{6.6}}$, the magnetic structure factor of such an orbital magnetic texture gives rise to two distinct magnetic responses at {\bf q}=0 and {\bf 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 ${\rm YBa_{2}Cu_{3}O_{6.9}}$ that exhibits the same {\bf q}=1/2 magnetism and a weakly overdoped ${\rm YBa_{2}Cu_{3}O_{7}}$ sample where this signal is no longer sizeable. The in-plane and out-of-plane magnetic neutron scattering intensities in ${\rm YBa_{2}Cu_{3}O_{6.9}}$ (at {\bf q}=1/2) and ${\rm YBa_{2}Cu_{3}O_{6.85}}$ (at {\bf q}=0), reported previously, display the same temperature dependent hallmarks. The magnitudes of both {\bf q}=0 and {\bf q}=1/2 magnetic signals further exhibit the same trends upon doping in ${\rm YBa_{2}Cu_{3}O_{6+x}}$, confirming that they are likely intertwined.