Resolving Phonons in Superconductor Bi2Sr2CaCu2O8+{\delta} at Sub-Unit-Cell Resolution

TL;DR

This study uses advanced electron energy loss spectroscopy to resolve layer-specific phonon modes in Bi2Sr2CaCu2O8+{eta}, revealing their spatial localization and modulation, which advances understanding of electron-phonon interactions in cuprate superconductors.

Contribution

It introduces sub-unit-cell resolved spectroscopy to identify and spatially map phonon modes in cuprates, linking lattice dynamics to superconducting properties.

Findings

Layer-specific phonon modes identified (~78 meV, ~42 meV, ~38 meV)

Phonon frequencies modulated by superstructure correlating with superconducting gap

Layer localization of phonons elucidated in complex cuprate lattice

Abstract

The role of phonons in cuprates remains controversial, with their complex lattice structure complicating the investigation. Here, we identify phonon modes originating from charge reservoir and superconducting layers of Bi2Sr2CaCu2O8+{\delta} using sub-unit-cell resolved electron energy loss spectroscopy in a scanning transmission electron microscope. We reveal several phonon modes exhibiting layer-specific localization: ~78 meV in-plane modes localized in the CuO2 planes, ~42 meV hybrid (in-plane and out-of-plane) modes in the CuO2 planes, and ~38 meV hybrid modes in the BiO layers. We also observe a periodic modulation of phonon frequencies induced by the superstructure, spatially correlating with the superconducting gap variation. Our findings offer new insights into the electron-phonon coupling in cuprates, fostering deeper exploration of the microscopic linkage between lattice dynamics and superconductivity.