Theoretical insights into electronic nematic order, bond-charge orders, and plasmons in cuprate superconductors

TL;DR

This paper reviews theoretical insights into charge-related phenomena in cuprate superconductors, including nematic and bond-charge orders and plasmons, highlighting the role of spin interactions and recent experimental correlations.

Contribution

It provides a comprehensive theoretical analysis of charge orders and plasmons in cuprates, emphasizing the dual energy structure and the relevance of the t-J and Hubbard models.

Findings

Nematic order driven by d-wave Pomeranchuk instability in hole-doped cuprates.

Resonant x-ray scattering data explained by d-wave bond-charge excitations in electron-doped cuprates.

Plasmon excitations match large-N t-J model predictions in both doping types.

Abstract

In this article, we focus on the charge degree of freedom in cuprate superconductors and review theoretical insights into the electronic nematic order, bond-charge orders, and plasmons. The low-energy charge dynamics is controlled by the spin-spin interaction J, which generates various bond-charge ordering tendencies including the electronic nematic order. The nematic order is driven by a d-wave Pomeranchuk instability and is pronounced in the underdoped region as well as around van Hove filling in the hole-doped case; the nematic tendency is weak in the electron-doped region. Nematicity consistent with the d-wave Pomeranchuk instability was reported for hole-doped cuprates in various experiments. Although the t-J and Hubbard models correctly predicted the proximity to the nematic instability in cuprates far before the experimental indications were obtained, full understanding of the charge ordering tendencies in hole-doped cuprates still requires further theoretical studies. In electron-doped cuprates, on the other hand, the d-wave bond-charge excitations around momentum q=(0.5pi,0) explain the resonant x-ray scattering data very well. Plasmon excitations are also present and the agreement between the large-N theory of the t-J model and resonant inelastic x-ray scattering measurements is nearly quantitative in both hole- and electron-doped cuprates. Theoretically the charge dynamics in cuprates is summarized as a dual structure in energy space: the low-energy region scaled by J, where the nematic and various bond-charge orders are relevant, and the high-energy region typically larger than J, where plasmons are predominant.