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

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 focused on a sharp ‘kink’ in the kinetic energy spectra of the electrons as a possible signature of the force that creates the superconducting state1,2,3,4,5,6,7,8,9,10,11,12,13,14. The kink has been related to a magnetic resonance13,15,16,17 and also to phonons18. Here we report that infrared spectra of Bi2Sr2CaCu2O8+δ (Bi-2212), shows 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 at this doping (Tc ≈ 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 provides a good candidate signature of the ‘glue’ that binds the electrons.