In the first part of my talk, I will list evidences supporting the existence of a Pair Density Wave (PDW) state in the pesudogap phase of cuprate. We observed a modulating gap in Bi2Sr2CaCu2O8+δ by using the Spectroscopic Imaging-Scanning Tunneling Microscopy (SI-STM) technique, proving the presence of a PDW order in this system. The gap modulation shows 8-unit-cell spatial periodicity along the Cu-O-Cu bond directions. We also observed local density of states modulating at 4-unit-cell and 8-unit-cell periodicities along the Cu-O-Cu bond directions. These density of states modulations can be understood as a coupling of the PDW order with itself and d-wave superconductivity respectively.
Then, I will present how the lattice in Bi2Sr2CaCu2O8+δ is coupled to the CDW order in the pseudogap phase. We directly visualize a spatial modulation of the lattice distortion that has the same periodicities with the unidirectional CDW orders, and furthermore we find that the lattice distortion always has a π out of phase locked-in with CDW order. Overall, our visualization of the PDW states and strong electron-lattice interactions here will help uncover the mysterious pesudogap phase of the cuprate.
Zengyi Du, et al., Nature 580, 6570 (2020) ;
Zengyi Du, et al., J. Phys. Soc. Jpn. 90, 111003 (2021);
Zengyi Du, et al., Physical Review X, 13, 021025(2023).