Visualizing the Cuprate Pair Density Wave State

Recently wide attention has been focused on the pair density wave (PDW) state in the cuprate high temperature superconductors. By implementing a novel superconducting tip technology in the spectroscopic imaging-scanning tunneling microscopy (SI-STM), we have observed a modulating gap with 8-unit-cell periodicity or at wavevectors Q=2π/a₀(1/8,0) and 2π/a₀(0,1/8) in the single particle tunneling on nearly optimally doped Bi₂Sr₂CaCu₂O_8+δ. This is the first spectroscopic evidence for a PDW to exist in the cuprates. We also observed induced density wave modulations in the local density-of-states N(r, E) at both Q and 2Q, which further supports the existence of the PDW that is intertwined with the spatially uniform d-wave superconductivity. By mapping density wave spatial phases, PDW spatial phases tend to change by π surrounding 2π topological defects found in the induced N(r,E) modulations at 2Q. This suggests a presence of the half vortex in the PDW state. In this talk, we will present a canonical signature of the PDW states in the cuprate.

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).