Reconstruction of the occupied and unoccupied electronic states driven by quantum charge fluctuations in electron doped cuprate superconductors

TL;DR

This study uses advanced spectroscopy to reveal charge fluctuation-driven electronic states in electron-doped cuprates, providing insights into their role in high-temperature superconductivity.

Contribution

It provides direct experimental evidence of quantum charge fluctuations affecting both occupied and unoccupied electronic states in cuprates.

Findings

Spectral features consistent with charge fluctuation excitations were observed.

Both occupied and unoccupied states show signatures of quantum charge fluctuations.

Results offer new insights into the electronic structure relevant to high-$T_c$ superconductivity.

Abstract

The origin of electron-boson interactions is central to understanding high-$T_c$ superconductivity in cuprates. While phonons and magnetic fluctuations are widely considered as candidates for mediating electron pairing, the role of charge fluctuations -- one of the fundamental electronic degrees of freedom -- remains unclear. Here, we investigate the electronic structure of the electron-doped cuprate Nd$_{2-x}$Ce$_x$CuO$_4$ using angle-resolved photoemission spectroscopy and angle-resolved inverse photoemission spectroscopy, which reveal the occupied and unoccupied states, respectively. We identify emergent spectral features on both occupied and unoccupied states that are consistent with excitations driven by quantum charge fluctuations. The results obtained in this study offer direct experimental insight into charge fluctuations in cuprates, thereby paving the way towards clarifying their fine electronic structure and the mechanism of high-$T_c$ superconductivity.