Eight-Unit-Cell Electronic Modulations in Cuprates Originating from Local Molecular Orbitals

The pair density wave state with eight-unit-cell (8a_{0}) periodicity has been widely regarded as the primary order in cuprates, yet its existence and origin remain subjects of intense debate. Using spectroscopic imaging scanning tunneling microscopy, we observe spatial modulations of the electronic states with approximately 8a_{0} periodicity in both the superconducting and insulating regimes of hole-doped Ca_{2}CuO_{2}Cl_{2} cuprate. We find that the 8a_{0} spatial patterns are generated by the formation of molecular orbitals by doped holes, which organize into 4a_{0}×4a_{0} plaquettes as the basic unit. Our results identify the 4a_{0} molecular-orbital plaquette as the fundamental electronic building block in cuprates, while the 8a_{0} pair density wave represents a spatial subharmonic that emerges at sufficiently high doping.