We discuss the crossover from the quantum critical, z = 1, to the quantum disordered regime in high-T c materials in relation to the experimental data on the nuclear relaxation, bulk susceptibility, and inelastic neutron scattering. In our scenario, the spin excitations develop a gap ∆ ∼ 1/ξ well above T c , which is supplemented by the quasiparticle gap below T c . The above experiments yield consistent estimates for the value of the spin gap, which increases as the correlation length decreases.

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