Anisotropy of Electronic Spin Texture in the High-Temperature Cuprate Superconductor Bi₂Sr₂CaCu₂O_8+δ

Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics. Here, by using spin- and angle-resolved photoemission spectroscopy, we confirm the helical spin texture caused by spin-layer locking in the nodal region in the cuprate superconductor Bi₂Sr₂CaCu₂O_8+δ and discover the anisotropy of spin polarizations at nodes along Γ–X and Γ–Y directions. The breaking of C₄ rotational symmetry in electronic spin texture may give deeper insights into understanding the ground state of cuprate superconductors.