[Paper Review] Angle-Resolved Photoemission Spectroscopy on Electronic Structure and Electron-Phonon Coupling in Cuprate Superconductors

X. J. Zhou, Tanja Cuk+3 more|arXiv (Cornell University)|Apr 11, 2006

Physics of Superconductivity and Magnetism4 citations

TL;DR

This paper uses angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic structure and electron-phonon coupling in cuprate superconductors, revealing strong, anisotropic electron-phonon interactions that vary with doping and momentum direction. Key findings include the emergence of polaronic behavior in underdoped compounds and anisotropic coupling to specific phonon modes, particularly the in-plane half-breathing mode, which may enhance d-wave pairing through vertex corrections.

ABSTRACT

This treatise reviews latest results obtained from angle-resolved photoemission spectroscopy (ARPES) on cuprate superconductors, with a special focus on the electron-phonon interaction. What has emerged is rich information about the anomalous electron-phonon interaction well beyond the traditional views of the subject. It exhibits strong doping, momentum and phonon symmetry dependence, and shows complex interplay with the strong electron-electron interaction in these materials.

Motivation & Objective

• To understand the role of electron-phonon coupling in high-Tc cuprates beyond conventional BCS theory.
• To investigate how electron-electron correlations and electron-phonon interactions coexist and influence each other in strongly correlated electron systems.
• To map the doping evolution of electronic structure and electron-phonon coupling across the phase diagram of cuprates.
• To determine whether electron-phonon coupling can contribute to d-wave superconductivity in the presence of strong correlations.
• To clarify the role of specific phonon modes, such as the half-breathing mode, in mediating electron-phonon interactions and affecting spectral features.

Proposed method

• Utilized high-resolution angle-resolved photoemission spectroscopy (ARPES) to probe the momentum- and energy-resolved electronic structure of cuprate superconductors.
• Measured quasiparticle dispersion and spectral weight evolution across different doping levels, from underdoped to overdoped regimes.
• Analyzed electron self-energy and spectral function to extract information on electron-phonon coupling strength and momentum dependence.
• Applied theoretical frameworks including weak-coupling perturbation theory, strong-coupling polaron models, and Migdal-Eliashberg theory to interpret ARPES data.
• Incorporated vertex corrections to electron-phonon coupling, particularly for off-diagonal couplings, to assess their impact on effective pairing interactions.
• Compared theoretical predictions with experimental spectra to assess the role of local Coulomb repulsion in suppressing charge density modulations and altering phonon contributions to resistivity and pairing.

Experimental results

Research questions

• RQ1 How does electron-phonon coupling vary with doping and momentum direction in cuprate superconductors?
• RQ2 To what extent do electron-phonon interactions contribute to d-wave superconductivity in the presence of strong electron-electron correlations?
• RQ3 What is the role of specific phonon modes, such as the in-plane half-breathing mode, in mediating electron-phonon coupling and influencing spectral features?
• RQ4 How do vertex corrections to electron-phonon coupling affect the anisotropy of the coupling and its potential role in pairing?
• RQ5 Why do underdoped cuprates exhibit polaronic behavior while optimally doped compounds show Migdal-Eliashberg-like spectra?

Key findings

• ARPES spectra in underdoped cuprates show strong polaronic features, indicating that carriers are best described as small polarons in a highly correlated, antiferromagnetic background.
• In optimally and overdoped cuprates, spectral features resemble the Migdal-Eliashberg picture, indicating a transition from polaronic to more conventional electron-phonon coupling behavior.
• Electron-phonon coupling is highly anisotropic, with stronger coupling along the antinodal direction (near (π,0)) and weaker coupling along the nodal direction (0,0)–(π,π), consistent with observed quasiparticle broadening.
• The in-plane half-breathing phonon mode exhibits a sharp softening with increasing hole doping and couples strongly to the Zhang-Rice singlet, potentially enhancing d-wave pairing via vertex corrections.
• Vertex corrections to electron-phonon coupling enhance the effective interaction for d-wave pairing, particularly for off-diagonal couplings, and are more pronounced in the electronic self-energy than in the phononic self-energy.
• Local Coulomb repulsion suppresses charge density modulations, reducing electron-phonon coupling at large momentum transfers and favoring small-q phonons, which may enhance d-wave pairing through increased effective coupling strength.