In this paper, we find that the strong correlation that exists in the high-${\mathit{T}}_{\mathit{c}}$ cuprate oxides can lead to both elastic and inelastic angle-resolved photoemission spectroscopies. In the elastic process the correlation only produces a normalizing factor to the matrix element of the photon-electron interaction; this term accounts for the peak, satisfies the sum rule, and has a superconducting gap. In the inelastic process the correlation can cause the photoelectrons to scatter inelastically with the charge and spin fluctuations and contributes a large background to the spectroscopy. In particular, the background does not satisfy the sum rule, so that the whole intensity is of non-sum-rule type. It also has an energy threshold in the superconducting state that results in a dip in the spectroscopy. Our theoretical predictions agree with the large background, non-sum-rule, and dip observed in the experiments.

• Received 29 December 1993

DOI:https://doi.org/10.1103/PhysRevB.49.13160