Atomic-Scale Visualization of the Cuprate Pair Density Wave State*

A Pair Density Wave (PDW) state brings up an attention to uncover the mysterious pesudogap states of the cuprate. Recently, we have observed a modulating gap in Bi₂Sr₂CaCu₂O_8+δ by the Spectroscopic Imaging-Scanning Tunneling Microscopy (SI-STM) technique, indicating a presence of the PDW order in this system¹. The gap modulation shows 8-unit-cell spatial periodicity along the Cu-O-Cu bond directions at the pesudogap energy. We also observed local density of states modulations at 4-unit-cell and 8-unit-cell periodicities along the Cu-O-Cu bond directions in the electronic structures. These results can be understood as a coupling of the PDW order itself inducing a CDW with 4-unit-cell periodicity, and a coupling between d-wave superconductivity and PDW order inducing a CDW with 8-unit-cell periodicity, respectively. In addition, we have identified edge dislocations (2p phase winding) in the CDW with 4-unit-cell periodicity, implying that there would be a p phase winding in the PDW order if they are coupled. Indeed, we observed the  p phase winding (a half-vortex) in the PDW order. Overall, we have observed canonical signatures of the PDW that is intertwined with the d-wave superconducting order. In this talk, we will discuss how they are related to each other in detail².

1, Zengyi Du, Hui Li, Sanghyun Joo, Elizabeth P. Donoway, Jinho Lee, J. C. Séamus Davis, Genda Gu, Peter D. Johnson & Kazuhiro Fujita, Nature 580 6570 (2020);

2, Zengyi Du, Hui Li, Kazuhiro Fujita, Journal of the Physical Society of Japan 90, 11103 (2021)