Dispersion Anomalies in Cuprate Superconductors

TL;DR

This paper explains the dispersion anomalies in cuprate superconductors as effects of electron interactions with collective spin excitations, highlighting differences between normal and superconducting states.

Contribution

It provides a unified explanation for dispersion features in cuprates based on electron-spin excitation interactions, contrasting with phonon-based explanations.

Findings

Normal state dispersion shows a crossover at spin fluctuation energies.

Superconducting state antinodal dispersion exhibits an S-shape linked to spin resonance.

Nodal dispersion features a kink due to non-resonant spin excitations.

Abstract

We argue that the shape of the dispersion along the nodal and antinodal directions in the cuprates can be understood as a consequence of the interaction of the electrons with collective spin excitations. In the normal state, the dispersion displays a crossover at an energy where the decay into spin fluctuations becomes relevant. In the superconducting state, the antinodal dispersion is strongly affected by the spin resonance and displays an S-shape whose magnitude scales with the resonance intensity. For nodal fermions, relevant spin excitations do not have resonance behavior, rather they are better characterized as a gapped continuum. As a consequence, the S-shape becomes a kink, and superconductivity does not affect the dispersion as strongly. Finally, we note that optical phonons typically lead to a temperature independent S-shape, in disagreement with the observed dispersion.