A phenomenological model of the Resonance peak in High Tc   Superconductors
  A notable aspect of high-temperature superconductivity in the copper oxides is the unconventional nature of the underlying paired-electron states. The appearance of a resonance peak, observed in inelastic neutron spectroscopy in the superconducting state of the High Tc cuprates, its apparent linear correlation with the critical superconducting temperature of each of the compounds and its disappearance in the normal state are rather intriguing. It may well be that this peak is the signature of the singlet to triplet excitation, and is an unique characteristic of a d-wave superconductor. We develop a simple criterion for the resonance peak which is based on the concept of twist sti ness and its disappearance at T=Tc. 
Benoy Chakraverty