Plasmon excitations in layered high-Tc cuprates

TL;DR

This paper investigates plasmon excitations in layered high-Tc cuprates using the t-J model, revealing how interlayer interactions influence plasmon dispersion and connecting theoretical predictions with recent RIXS experimental observations.

Contribution

It introduces a detailed theoretical analysis of plasmon modes in layered cuprates, incorporating interlayer hopping and Coulomb interactions, and relates findings to recent experimental data.

Findings

Plasmon modes exist above the particle-hole continuum.

Interlayer hopping significantly affects plasmon dispersion near q=(0,0).

RIXS-observed modes can be identified as finite-qz plasmons.

Abstract

Motivated by the recent resonant inelastic x-ray scattering (RIXS) experiment for the electron-doped cuprates Nd_{2-x}Ce_{x}CuO_{4} with x around 0.15, we compute the density-density correlation function in the t-J model on a square lattice by including interlayer hopping and the long-range Coulomb interaction. We find that collective charge excitations are realized not inside the particle-hole continuum, but above the continuum as plasmons. The plasmon mode has a rather flat dispersion near the in-plane momentum q=(0,0) with a typical excitation energy of the order of the intralayer hopping t when the out-of-plane momentum qz is zero. However, when qz becomes finite, the plasmon dispersion changes drastically near q=(0,0), leading to a strong dispersive feature with an excitation gap scaled by the interlayer hopping tz. We discuss that the mode recently observed by RIXS near q=(0,0) can be associated with the plasmon mode with a finite qz.