Asymmetry of collective excitations in electron and hole doped cuprate superconductors

TL;DR

This study reveals fundamental differences in high-energy magnetic excitations between electron- and hole-doped cuprate superconductors, challenging existing theories and providing new insights into the mechanisms of high-temperature superconductivity.

Contribution

It uncovers the asymmetry of collective magnetic excitations in electron- and hole-doped cuprates using resonant inelastic x-ray scattering, highlighting differences in magnetic behavior and emergent modes.

Findings

Magnetic excitations harden across the AFM-HTSC boundary in NCCO.

An unexpected dispersive mode appears in electron-doped NCCO.

High-energy excitations differ significantly between electron- and hole-doped cuprates.

Abstract

High-temperature superconductivity (HTSC) mysteriously emerges upon doping holes or electrons into insulating copper oxides with antiferromagnetic (AFM) order. It has been thought that the large energy scale of magnetic excitations, compared to phonon energies for example, lies at the heart of an electronically-driven superconducting phase at high temperatures. However, despite extensive studies, little information is available for comparison of high-energy magnetic excitations of hole- and electron-doped superconductors to assess a possible correlation with the respective superconducting transition temperatures. Here, we use resonant inelastic x-ray scattering (RIXS) at the Cu L3-edge to reveal high-energy collective excitations in the archetype electron-doped cuprate Nd2-xCexCuO4 (NCCO). Surprisingly, despite the fact that the spin stiffness is zero and the AFM correlations are short-ranged, magnetic excitations harden significantly across the AFM-HTSC phase boundary, in stark contrast with the hole-doped cuprates. Furthermore, we find an unexpected and highly dispersive mode in superconducting NCCO that is undetected in the hole-doped compounds, which emanates from the zone center with a characteristic energy comparable to the pseudogap, and may signal a quantum phase distinct from superconductivity. The uncovered asymmetry in the high-energy collective excitations with respect to hole and electron doping provides additional constraints for modeling the HTSC cuprates.