A large body of spectroscopic data on the cuprate high temperature superconductors (CHTSC) is reviewed in order to determine their order parameter. ASJ, INS, B2g Raman spectra, optical data, NIS "dips", ARPES "dips" and ARPES "kinks" all show the same excitation energy (40 meV for OP95 systems), proportional to the superconducting transition temperature, and it is therefore identified with the order parameter.
@article{arxiv.0911.0827,
title = {Remarks on the Order Parameter of the Cuprate High Temperature Superconductors},
author = {Stefan Huefner and Frank Mueller},
journal= {arXiv preprint arXiv:0911.0827},
year = {2015}
}