Charge-Stripe Crystal Phase in an Insulating Cuprate

TL;DR

This study reveals a unidirectional charge-stripe order in lightly-doped insulating cuprates, providing crucial insights into the electronic phases preceding pseudogap formation and high-temperature superconductivity.

Contribution

It demonstrates the existence of an insulating charge-stripe crystal phase in a cuprate, observed via spectroscopic imaging, extending understanding of charge order in the doping process.

Findings

Discovery of a unidirectional charge-stripe order with 4a0 period

Charge-stripe phase develops before pseudogap and Fermi surface formation

Observation achieved in lightly-doped Bi2Sr2CaCu2O8+x using surface annealing

Abstract

High-Tc superconductivity in cuprates is generally believed to arise from carrier doping an antiferromagnetic Mott (AFM) insulator. Theoretical proposals and emerging experimental evidence suggest that this process leads to the formation of intriguing electronic liquid crystal phases. These phases are characterized by ordered charge and/or spin density modulations, and thought to be intimately tied to the subsequent emergence of superconductivity. The most elusive, insulating charge-stripe crystal phase is predicted to occur when a small density of holes is doped into the charge-transfer insulator state, and would provide a missing link between the undoped parent AFM phase and the mysterious, metallic pseudogap. However, due to experimental challenges, it has been difficult to observe this phase. Here, we use surface annealing to extend the accessible doping range in Bi-based cuprates and achieve the lightly-doped charge-transfer insulating state of a cuprate Bi2Sr2CaCu2O8+x. In this insulating state with a charge transfer gap at the order of ~1 eV, using spectroscopic-imaging scanning tunneling microscopy, we discover a unidirectional charge-stripe order with a commensurate 4a0 period along the Cu-O-Cu bond. Importantly, this insulating charge-stripe crystal phase develops before the onset of the pseudogap and the formation of the Fermi surface. Our work provides new insights into the microscopic origin of electronic inhomogeneity in high-Tc cuprates.