# Doping evolution of the charge excitations and electron correlations in electron-doped superconducting La$_{2-x}$Ce$_{x}$CuO$_{4}$

## TL;DR

This study uses resonant inelastic x-ray scattering to investigate how charge excitations and electron correlations evolve with doping in electron-doped cuprate superconductor La$_{2-x}$Ce$_{x}$CuO$_{4}$, revealing a transition from incoherent to coherent electronic states.

## Contribution

It provides new insights into the doping-dependent evolution of charge excitations and electron correlations in La$_{2-x}$Ce$_{x}$CuO$_{4}$ using RIXS, highlighting the transition from incoherent to coherent quasiparticles.

## Key findings

- Plasmons are identified as 3D charge excitations.
- Plasmon energy increases monotonically with doping.
- Evolution from broad to sharp plasmon peaks indicates increasing electron coherence.

## Abstract

Electron correlations play a dominant role in the charge dynamics of the cuprates. We use resonant inelastic x-ray scattering (RIXS) to track the doping dependence of the collective charge excitations in electron doped La$_{2-x}$Ce$_{x}$CuO$_{4}$(LCCO). From the resonant energy dependence and the out-of-plane momentum dependence, the charge excitations are identified as three-dimensional (3D) plasmons, which reflect the nature of the electronic structure and Coulomb repulsion on both short and long length scales. With increasing electron doping, the plasmon excitations show monotonic hardening in energy, a consequence of the electron correlation effect on electron structure near the Fermi surface (FS). Importantly, the plasmon excitations evolve from a broad feature into a well defined peak with much increased life time, revealing the evolution of the electrons from incoherent states to coherent quasi-particles near the FS. Such evolution marks the reduction of the short-range electronic correlation, and thus the softening of the Mottness of the system with increasing electron doping.