High-transition-temperature superconductivity in the absence of the magnetic-resonance mode

TL;DR

This study shows that the magnetic resonance mode and phonons are unlikely to be the main cause of high-Tc superconductivity in cuprates, suggesting the broad background spectrum as a potential 'glue' for electron pairing.

Contribution

It demonstrates that the magnetic resonance mode disappears before the superconducting transition temperature drops significantly, challenging previous theories about its role in high-Tc superconductivity.

Findings

Magnetic resonance mode weakens with doping and vanishes at critical doping level 0.23.

Superconductivity remains strong despite the disappearance of the resonance mode.

Broad background in infrared spectra persists and may be responsible for electron pairing.

Abstract

The fundamental mechanism that gives rise to high-transition-temperature (high-Tc) superconductivity in the copper oxide materials has been debated since the discovery of the phenomenon. Recent work has focussed on a sharp 'kink' in the kinetic energy spectra of the electrons as a possible signature of the force that creates the superconducting state. The kink has been related to a magnetic resonance and also to phonons. Here we report that infrared spectra of Bi2Sr2CaCu2O(8+d), (Bi-2212) show that this sharp feature can be separated from a broad background and, interestingly, weakens with doping before disappearing completely at a critical doping level of 0.23 holes per copper atom. Superconductivity is still strong in terms of the transition temperature (Tc approx 55 K), so our results rule out both the magnetic resonance peak and phonons as the principal cause of high-Tc superconductivity. The broad background, on the other hand, is a universal property of the copper oxygen plane and a good candidate for the 'glue' that binds the electrons.