Spin-charge separation is the key to the high Tc cuprates

The most striking fact about the high-T-c cuprates is that in none of the r elevant regions of the phase diagram is there any evidence of the usual eff ects of phonon or impurity scattering. This is strong evidence that these s tates are in a "quantum protectorate" to burrow Laughlin's terms. (Two stri king experimental facts which demonstrate this are the absence of phonon se lf-energy in ARPES measurements, demonstrated recently by Johnson in BSCCO [1], and the scattering-independent T-c in YBCO, even though the supercondu ctivity is d-wave.) A quantum protectorate is a state in which the many-bod y correlations are so strong that the dynamics can no longer be described i n terms of individual particles, and therefore perturbations which scatter individual particles are not effective.