Coexistence of Two Sharp-Mode Couplings and Their Unusual Momentum Dependence in the Superconducting State of Bi2Sr2CaCu2O8+d Superconductor Revealed by Laser-Based Angle-Resolved Photoemission

TL;DR

This study uses laser-based ARPES to reveal two coexisting sharp electron-boson coupling modes with distinct momentum dependencies in Bi2212 superconductors, challenging existing theories of high-temperature superconductivity.

Contribution

It uncovers the simultaneous presence of two energy scales with unique momentum behaviors in the superconducting state of Bi2212, providing new insights into electron-mode interactions.

Findings

Two coexisting energy scales observed in Bi2212 superconductors.

One mode remains at ~78 meV across momentum space.

The other mode varies from ~40 meV to ~70 meV from antinodal to nodal regions.

Abstract

Super-high resolution laser-based angle-resolved photoemission measurements have been carried out on Bi2Sr2CaCu2O8+d (Bi2212) superconductors to investigate momentum dependence of electron coupling with collective excitations (modes). Two coexisting energy scales are clearly revealed over a large momentum space for the first time in the superconducting state of an overdoped Bi2212 superconductor. These two energy scales exhibit distinct momentum dependence: one keeps its energy near 78 meV over a large momentum space while the other changes its energy from $\sim$40 meV near the antinodal region to $\sim$70 meV near the nodal region. These observations provide a new picture on momentum evolution of electron-boson coupling in Bi2212 that electrons are coupled with two sharp modes simultaneously over a large momentum space in the superconducting states. Their unusual momentum dependence poses a challenge to our current understanding of electron-mode-coupling and its role for high temperature superconductivity in cuprate superconductors.