# Charge-stripe crystal phase in an insulating cuprate

## Abstract

High-temperature (high-Tc) superconductivity in cuprates arises from carrier doping of an antiferromagnetic Mott insulator. This carrier doping leads to the formation of electronic liquid-crystal phases1. The insulating charge-stripe crystal phase is predicted to form when a small density of holes is doped into the charge-transfer insulator state1,2,3, 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 Bi2Sr2CaCu2O8+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 4a0 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-Tc cuprates.

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## Data availability

The data supporting the findings of this study are available upon request from the corresponding author.

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## Acknowledgements

The authors thank M. Allan, J.C. Davis, J.E. Hoffman, S. Kivelson and S. Sachdev for insightful conversations. I.Z. acknowledges support from DARPA grant no. N66001-17-1-4051 (Z.R.), Army Research Office grant no. W911NF-17-1-0399 (B.R.), National Science Foundation grant no. NSF-DMR-1654041 (H.Z.) and the Boston College startup. Z.W. acknowledges support from the US Department of Energy, Basic Energy Sciences grant no. DE-FG02-99ER45747. The work in Brookhaven was supported by the Office of Science, US Department of Energy under contract no. DE-SC0012704. J.S. and R.Z. were supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science.

## Author information

STM experiments were carried out by H.Z. Magnetization measurements were performed by Z.R. Temperature-dependent reflection high-energy electron diffraction measurements and heater calibration were carried out by B.R. Single crystals of optimally doped Bi-2212 were obtained from J.S., R.Z. and G.G. H.Z. analysed the STM data with guidance from I.Z. I.Z. designed and supervised the project. Z.W. provided theoretical input on the interpretation of STM data. I.Z. and Z.W. wrote the manuscript with input from all the authors.

Correspondence to Ilija Zeljkovic.

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### Competing interests

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## Supplementary information

### Supplementary Information

Supplementary Sections 1–8, Supplementary Figures 1–11, Supplementary References 1–16

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• #### DOI

https://doi.org/10.1038/s41563-018-0243-x

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