Theoretical perspectives on charge dynamics in high-temperature cuprate superconductors

TL;DR

This review discusses recent theoretical advances in understanding charge dynamics in high-temperature cuprate superconductors, highlighting collective behaviors like plasmons and charge order tendencies across different doping types.

Contribution

It introduces a unified theoretical framework incorporating layered structure and Coulomb interactions to explain charge excitations and order phenomena in cuprates.

Findings

Acousticlike plasmons are observed universally in cuprates.

D-wave bond-charge order tendencies are prominent in electron-doped cuprates.

Charge-order signatures are also present in hole-doped cuprates, but are not fully explained by current models.

Abstract

We review recent theoretical progress on the charge dynamics of doped carriers in high-temperature cuprate superconductors. Advances in this field have clarified that doped charges in cuprates exhibit remarkably rich collective behavior, governed by the combined effects of strong electronic correlations, the intrinsic layered crystal structure, and long-range Coulomb interaction. First, the emergence of acousticlike plasmons has been firmly established through quantitative analyses of resonant inelastic x-ray scattering (RIXS) spectra based on the t-J-V model -- an extension of the conventional t-J model that incorporates the layered crystal structure and the long-range Coulomb interaction V. These acousticlike plasmons arise near the in-plane momentum q=(0,0) and possess characteristic energies far below the well-known ~ 1 eV optical plasmon. This behavior is found to be universal across both hole- and electron-doped cuprates, including multilayer systems. Second, in electron-doped cuprates, a pronounced tendency toward d-wave bond-charge order develops near q=(0.5pi, 0), as revealed by resonant x-ray scattering (RXS) and RIXS. As a result, the charge dynamics acquires a dual structure, in which low-energy bond-charge excitations coexist with relatively high-energy plasmons. Third, analogous signatures of charge-order tendency have also been reported in hole-doped cuprates. However, a direct application of the d-wave bond-charge-order framework fails to account for experimental observations. Similarly, the charge-stripe order in La-based cuprates remains unresolved within existing theoretical approaches. Assuming that mobile carriers behave in a largely universal manner across electron- and hole-doped systems, we discuss a possible scenario that may reconcile these diverse experimental findings.