Electron self-energy of high temperature superconductors as revealed by angle-resolved photoemission

In this paper, we review some of the work our group has done in the past fe w years to obtain the electron self-energy of high temperature superconduct ors by analysis of angle-resolved photoemission data. We focus on three exa mples which have revealed: (1) a d-wave superconducting gap, (2) a collecti ve mode in the superconducting state, and (3) pairing correlations in the p seudogap phase. In each case, although a novel result is obtained which cap tures the essence of the data, the conventional physics used leads to an in complete picture. This indicates that new physics needs to be developed to obtain a proper understanding of these materials. (C) 1998 Elsevier Science Ltd. All rights reserved.