Charge-stripe crystal phase in an insulating cuprate

High-temperature (high- T c ) superconductivity in cuprates arises from carrier doping of an antiferromagnetic Mott insulator. This carrier doping leads to the formation of electronic liquid-crystal phases 1 . The insulating charge-stripe crystal phase is predicted to form when a small density of holes is doped into the charge-transfer insulator state 1 – 3 , but this phase is yet to be observed experimentally. Here, we use surface annealing to extend the accessible doping range in Bi-based cuprates and realize the lightly doped charge-transfer insulating state of the cuprate Bi 2 Sr 2 CaCu 2 O 8+ x . In this insulating state with a charge transfer gap on the order of ~1 eV, our spectroscopic imaging scanning tunnelling microscopy measurements provide strong evidence for a unidirectional charge-stripe order with a commensurate 4 a 0 period along the Cu–O–Cu bond. Notably, this insulating charge-stripe crystal phase develops before the onset of the pseudogap and formation of the Fermi surface. Our work provides fresh insight into the microscopic origin of electronic inhomogeneity in high- T c cuprates. A surface annealing method is used to access an insulating phase of Bi 2 Sr 2 CaCu 2 O 8+ x and unidirectional charge order is observed.