Doping dependence of low-energy charge collective excitations in high-T$_c$ cuprates

TL;DR

This paper investigates how doping levels affect low-energy charge excitations in high-Tc cuprates, revealing new plasmon modes and their evolution near optimal doping, with implications for understanding high-temperature superconductivity.

Contribution

It introduces the existence of three anomalous plasmon branches, including hyperplasmons and a 1D plasmon mode, and provides an analytic response function considering full band dispersion.

Findings

Identification of three anomalous plasmon branches in cuprates.

Doping significantly alters the properties of these modes near optimal doping.

Derivation of an analytic expression for the dynamic response function.

Abstract

In this study, we analyze the dielectric function of high-Tc cuprates as a function of doping level, taking into account the full energy band dispersion within the CuO$_2$ monolayer. In addition to the conventional two-dimensional (2D) gapless plasmon mode, our findings reveal the existence of three anomalous branches within the plasmon spectrum. Two of these branches are overdamped modes, designated as hyperplasmons, and the third is an almost one-dimensional plasmon mode (1DP). We derive an analytic expression for dynamic part of the response function. Furthermore, we investigated the effect of the doping on these modes. Our analysis demonstrates that in the doping level range close to the optimal doping level, the properties of all three modes undergo a significant transformation.