Persistence of Strong Electron Coupling to a Narrow Boson Spectrum in Overdoped BiSrCaCuO (Bi2212) Tunneling Data

TL;DR

This study uses tunneling spectroscopy and Eliashberg analysis to show that strong electron coupling to a narrow boson spectrum persists in overdoped Bi2212, challenging previous optical conductivity findings and highlighting the technique's sensitivity to pairing interactions.

Contribution

It demonstrates that the narrow boson spectrum remains significant in overdoped Bi2212, providing new insights into the pairing mechanism in high-temperature superconductors.

Findings

The tunneling dip feature is linked to strong electron-boson coupling.

The narrow boson spectrum persists in overdoped Bi2212 with Tc of 56-62 K.

Discrepancies with optical measurements are explained by different self-energy sensitivities.

Abstract

A d-wave, Eliashberg analysis of break junction and STM tunneling spectra on BiSrCaCuO (Bi2212) reveals that a spectral dip feature is directly linked to strong electronic coupling to a narrow boson spectrum, evidenced by a large peak in the boson spectral weight. The tunneling dip feature remains robust in the overdoped regime of Bi2212 with bulk Tc values of 56 K-62 K. This is contrary to recent optical conductivity measurements of the self-energy that suggest the narrow boson spectrum disappears in overdoped Bi2212 and therefore cannot be essential for the pairing mechanism. The discrepancy is resolved by considering the way each technique probes the electron self-energy, in particular, the unique sensitivity of tunneling to the off-diagonal or pairing part of the self-energy.