Common magnetic origin of the resonance peak and incommensuration in high-T-c superconductors

We present a unified theory for the resonance peak and low-energy incommens urate response observed in high-T-c cuprate superconductors. The origin of both features is purely magnetic and they represent universal features sign aling the existence of an incommensurate spin state both below and above th e superconducting transition temperature. We argue that the resonance peak is the reflection of commensurate antiferromagnetism. Our theoretical scena rio gives an account of the main universal features observed in various fam ilies of superconductors and predicts those that have not been observed yet experimentally.