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Abstract:

We study the magnetic response properties of both site and spatially disordered Anderson-Hubbard models via a random-phase-type approximation for collective excitations about stable, inhomogeneous mean-field ground states. For the site-disordered model, zero-temperature transitions between paramagnetic, disordered antiferromagnetic and spin-glass-like ground states are examined. Within broken symmetry phases, a microscopic picture of the response of the inhomogeneous distribution of local magnetic moments to an external field is obtained, and the role of disorder in leading to a strong site differential enhancement in local susceptibilities is highlighted.

Abstract:

We present a microscopic description of the inhomogeneous magnetic response of a disordered, interacting system, with local susceptibilities determined via a random-phase-approximation-type approach about stable, inhomogeneous mean-field ground states. A careful treatment of the role of disorder is vital in describing: the phase boundary to local moment formation; site-differential inhomogeneity in the distribution of local susceptibilities in a local moment regime, and its marked disorder-induced enhancement; and, on the length scales probed, large disorder-induced fluctuations in the total magnetic susceptibility. © 1995 The American Physical Society.

Abstract:

A novel and physically transparent approach to the finite-temperature Hubbard model at half filling is proposed. It recovers not only the correct dimensionality dependence of antiferromagnetism but, in d=3, interpolates properly between weak and strong coupling interaction strengths for the Néel temperature, and enables extraction of related thermodynamic properties. © 1995 The American Physical Society.

Abstract:

We discuss an Onsager reaction field approach to the paramagnetic phase of a spatially anisotropic Heisenberg model, with nearest-neighbor in-plane (J) and interplane (J) exchange couplings. The theory is physically transparent and, together with the use of suitable asymptotic approximations, provides a simple, consistent description of the crossover from effective two- to three-dimensional behavior, and captures well both the pure d=2 (=0) and d=3 (J=J) dimensional limits. Application to La2CuO4 is briefly considered. © 1995 The American Physical Society.