Collective Modes in High-Temperature Superconductors

TL;DR

This paper investigates the role of collective modes in high-temperature cuprate superconductors, linking theoretical calculations to experimental observations in neutron scattering, ARPES, and Raman spectra.

Contribution

It demonstrates that specific collective modes explain key features observed in experiments on cuprates, using the FLEX approximation for the Hubbard model.

Findings

Large peak in spin susceptibility from a spin-density-wave mode

Dip in ARPES spectrum due to collective mode

Broad peak in Raman spectrum from amplitude fluctuation of the d-wave gap

Abstract

The role of collective modes in various experiments on the cuprates is investigated. We calculate the neutron scattering, photoemission (ARPES), and Raman scattering intensities below $T_c$ within the fluctuation-exchange (FLEX) approximation for the two-dimensional Hubbard model. It is shown that the large peak in the dynamical spin susceptibility arises from a weakly damped spin-density-wave collective mode. This gives rise to a dip between the sharp low energy peak and the higher binding energy hump in the ARPES spectrum. Furthermore, we show that the collective mode of the amplitude fluctuation of the d-wave gap yields a broad peak above the pair-breaking threshold in the $B_{1g}$ Raman spectrum.