# Mode-selective coupling of coherent phonons to the Bi2212 electronic band structure

## TL;DR

This study uses time- and angle-resolved photoemission spectroscopy to observe mode-selective coherent phonons in a cuprate superconductor, revealing specific phonon-electron coupling dynamics near the Fermi level.

## Contribution

It demonstrates mode-selective coupling of coherent phonons to the electronic band structure in Bi2212, identifying specific CuO2-derived phonons involved.

## Key findings

- Observed sub-meV band modulations at 3.94 and 5.59 THz.
- Identified the dominant mode as a CuO2-derived A1g phonon.
- Bi- and Sr-derived A1g modes are absent in measurements.

## Abstract

Cuprate superconductors host a multitude of low-energy optical phonons. Using time- and angle-resolved photoemission spectroscopy, we study coherent phonons in Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+\delta}$. Sub-meV modulations of the electronic band structure are observed at frequencies of $3.94\pm 0.01$ and $5.59\pm 0.06$ THz. For the dominant mode at 3.94 THz, the amplitude of the band energy oscillation weakly increases as a function of momentum away from the node. Theoretical calculations allow identifying the observed modes as CuO$_{2}$-derived $A_{1g}$ phonons. The Bi- and Sr-derived $A_{1g}$ modes which dominate Raman spectra in the relevant frequency range are absent in our measurements. This highlights the mode-selectivity for phonons coupled to the near-Fermi-level electrons, which originate from CuO$_{2}$ planes and dictate thermodynamic properties.