Magnetic scaling in cuprate superconductors

Abstract

We determine the magnetic phase diagram for the YBa2Cu3O6+x and La2−xSrxCuO4 systems from various NMR experiments. We discuss the possible interpretation of NMR and neutron scattering experiments in these systems in terms of both the nonlinear σ model of nearly localized spins and a nearly antiferromagnetic Fermi liquid description of magnetically coupled quasiparticles. We show for both the 2:1:4 and 1:2:3 systems that bulk properties, such as the spin susceptibiltiy, and probes at the antiferromagnetic wave vector (π,π), such as 63T1, the Cu63 spin-lattice relaxation time, both display a crossover at a temperature Tcr, which increases linearly with decreasing hole concentration, from a nonuniversal regime to a z=1 scaling regime characterized by spin pseudogap behavior. We pursue the consequences of the ansatz that Tcr corresponds to a fixed value of the antiferromagnetic correlation length ξ and show how this enables one to extract the magnitude and temperature dependence of ξ from measurements of T1 alone. We show that like Tcr, the temperature T* which marks a crossover at low temperatures from the z=1 scaling regime to a quantum disordered regime, exhibits the same dependence on doping for the 2:1:4 and 1:2:3 systems, and so arrive at a unified description of magnetic behavior in the cuprates, in which the determining factor is the planar hole concentration.

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