Evolution of the Spin Susceptibility of High-$T_c$ Superconductors

TL;DR

This paper introduces a model-independent numerical method to extract magnetic excitation spectra in high-$T_c$ superconductors, revealing temperature-dependent spectral weight transfer linked to magnetic origins of superconductivity.

Contribution

The study presents a novel, model-independent numerical Eliashberg inversion technique using maximum entropy to analyze optical self-energy data in high-$T_c$ superconductors.

Findings

Magnetic mode in Bi-2212 evolves from spectral weight transfer.

Spectral weight transfer begins at 200 K in optimally doped samples.

Overdoped samples show weaker spectral weight transfer.

Abstract

We demonstrate that a new tool, a model independent numerical Eliashberg inversion of the optical self-energy, based on maximum entropy considerations can be used to extract the magnetic excitation spectra of high-transition-temperature superconductors. In Bi-2212 we explicitly show that the magnetic mode that dominates the self-energy at low temperatures directly evolves out of a smooth transfer of spectral weight to the mode from the continuum just above it. This redistribution starts already at 200 K in optimally doped materials but is much weaker in overdoped samples. This provides evidence for the magnetic origin of the superconductivity and presents a challenge to theories of the spin susceptibility and to neutron scattering experiments in high-temperature superconductors.