Rapid change of superconductivity and electron-phonon coupling through 19% doping in Bi2212

TL;DR

This study reveals a rapid increase in electron-phonon coupling and superconducting gap in Bi2212 with 19% doping, indicating a close link between lattice interactions and superconductivity in the strange metal regime.

Contribution

It demonstrates a strong correlation between superconducting gap and electron-phonon coupling near the Brillouin zone boundary in doped Bi2212, highlighting their entanglement in the strange metal phase.

Findings

Electron-phonon coupling strength increases rapidly with doping.

Superconducting gap quadruples across the pseudogap boundary.

Lattice and electronic responses become entangled in the strange metal regime.

Abstract

Electron-boson coupling plays a key role in superconductivity for many systems. However, in copper-based high-temperature ($T_c$) superconductors, its relation to superconductivity remains controversial despite strong spectroscopic fingerprints. Here we use angle-resolved photoemission spectroscopy to find a striking correlation between the superconducting gap and the bosonic coupling strength near the Brillouin zone boundary in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The bosonic coupling strength rapidly increases from the overdoped Fermi-liquid regime to the optimally doped strange metal, concomitant with the quadrupled superconducting gap and the doubled gap-to-Tc ratio across the pseudogap boundary. This synchronized lattice and electronic response suggests that the effects of electronic interaction and the electron-phonon coupling become intimately entangled upon entering the strange metal regime, which may in turn drive a stronger superconductivity.