Doping dependence of the electron-phonon and electron-spin fluctuation interactions in the high-$T_{c}$ superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$

TL;DR

This study uses ultrafast optical techniques to investigate how electron interactions with phonons and spin fluctuations vary with doping in a high-temperature superconductor, revealing their distinct doping-dependent behaviors.

Contribution

It identifies and distinguishes the doping-dependent electron-phonon and electron-spin fluctuation couplings in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+eta}$ using ultrafast spectroscopy, highlighting their roles in superconductivity.

Findings

Electron-phonon coupling peaks at optimal doping.

Electron-spin fluctuation coupling decreases monotonically with doping.

Superconductivity's relation to antiferromagnetism and lattice effects.

Abstract

Using ultrafast optical techniques, we detect two types of bosons strongly coupled to electrons in the family of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ from the underdoped to overdoped regimes. The different doping dependences of the electron-boson coupling strengths enables us to identify them as phonons and spin fluctuations: electron-phonon coupling ($\lambda_{e-ph}$) peaks at optimal doping, and electron-spin fluctuation coupling ($\lambda_{e-sf}$) decreases monotonically with doping. This observation is consistent with two facts: (1) superconductivity is in close proximity with antiferromagnetism at low dopings, and (2) a pronounced lattice renormalization effect at larger dopings.