Atomically-resolved interlayer charge ordering and its interplay with superconductivity along the c direction in YBa₂Cu₃O_6.81

Charge order (CO) has been recognized as one of the most important competing order in superconductive cuprates. However, the most fundamental physical mechanisms governing CO, for example, the role of so-called charge reservoir (Cu-O chain) layers in CO and the spatial interplay of CO and SC, in highly-doped YBCO are still unclear.

Here, we present the direct real-space cross-sectional scanning tunneling microscopy (XSTM) imaging with atomic resolution to characterize the atomically resolved electronic structure along the c [001] direction in high-temperature superconductive YBa₂Cu₃O_6.81 cuprates. We demonstrate that CO occurs on CuO plane and chain layers with an antiphase correlation along the c-axis direction governed by Coulomb repulsion rather than Josephson tunneling. Similarly, superconductive coherence is also observed in chain and plane layers in YBa₂Cu₃O_6.81. In addition, at the CO phase boundary, the mutually competing behavior between CO and SC phases and a proximity-like boundary region are observed.

The present atomically-resolved XSTM provides a detailed insight into the unexplored interlayer coupling and its spatial interplay with superconductivity and therefore offers a new approach to unravel the fundamental physical mechanisms of superconductivity in cuprates.[1]