Magnetic fluctuations in n-type high-$T_c$ superconductors reveal breakdown of fermiology

TL;DR

This study shows that the conventional fermiology approach fails to explain magnetic fluctuations in electron-doped high-$T_c$ superconductors, indicating a need for alternative theories that consider quantum competition between magnetic and superconducting states.

Contribution

The paper combines experimental and theoretical analysis to demonstrate the breakdown of fermiology in describing magnetic fluctuations in electron-doped cuprates, highlighting the importance of quantum effects.

Findings

Fermiology predicts a step-like feature instead of a sharp resonance peak.

It underestimates the resonance intensity by an order of magnitude.

Most spectral weight is expected in incommensurate wings, which are not observed in electron-doped cuprates.

Abstract

By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr$_{0.88}$LaCe$_{0.12}$CuO$_4$ with theoretical calculations we demonstrate that the conventional fermiology approach cannot possibly account for the magnetic fluctuations in these materials. In particular, we perform tunneling experiments on the very same sample for which a dynamical magnetic resonance has been reported recently and use photoemission data by others on a similar sample to characterize the fermionic quasiparticle excitations in great detail. We subsequently use this information to calculate the magnetic response within the conventional fermiology framework as applied in a large body of work for the hole-doped superconductors to find a profound disagreement between the theoretical expectations and the measurements: this approach predicts a step-like feature rather than a sharp resonance peak, it underestimates the intensity of the resonance by an order of magnitude, it suggests an unreasonable temperature dependence of the resonance, and most severely, it predicts that most of the spectral weight resides in incommensurate wings which are a key feature of the hole-doped cuprates but have never been observed in the electron-doped counterparts. Our findings strongly suggest that the magnetic fluctuations reflect the quantum-mechanical competition between antiferromagnetic and superconducting orders.