Quantum disordered regime and spin gap in the cuprate superconductors

Abstract

We discuss the crossover from the quantum critical, z=1, to the quantum disordered regime in high-${\mathit{T}}_{\mathit{c}}$ 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 Δ∼1/ξ well above ${\mathit{T}}_{\mathit{c}}$, which is supplemented by the quasiparticle gap below ${\mathit{T}}_{\mathit{c}}$. The above experiments yield consistent estimates for the value of the spin gap, which increases as the correlation length decreases.