1. Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
2. Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000, USA

Correspondence to: T. Timusk¹ Correspondence and requests for materials should be addressed to T.T. (Email: timusk@mcmaster.ca).

Abstract

The fundamental mechanism that gives rise to high-transition-temperature (high-T_c) 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 state^{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}. The kink has been related to a magnetic resonance^{13, 15, 16, 17} and also to phonons¹⁸. Here we report that infrared spectra of Bi₂Sr₂CaCu₂O₈₊ (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 (T_c 55 K), so our results rule out both the magnetic resonance peak and phonons as the principal cause of high-T_c 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.

1. Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
2. Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000, USA

Correspondence to: T. Timusk¹ Correspondence and requests for materials should be addressed to T.T. (Email: timusk@mcmaster.ca).

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