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Abstract:

The dynamics of a single hole in the t-J model is solved exactly for all temperature, T, in the limit of large spatial dimensions, d = ∞, using the Feenberg renormalized perturbation series. We focus in particular on single-particle spectra, together with optical and static hole conductivities. Explicit results are illustrated for a Bethe lattice, and exemplify the continuous thermal evolution of the underlying string picture from the T = 0 string-pinned limit through to the paramagnetic phase. Quenched site-disorder is also readily incorporated, exact results thereby being obtained for the interplay between disorder and thermally-induced hole dynamics.

Abstract:

A microscopic three-band Anderson-Mott-Hubbard model for cubic disordered tungsten bronzes (Formula presented) and (Formula presented) is studied over a range of doping levels (Formula presented) at the level of an unrestricted Hartree-Fock approximation in order to understand the effects of disorder and electron interaction on the electronic ground state and their implications for the chemically induced metal-insulator transition observed at least in the latter materials. For sufficiently large U a pseudogap develops at (Formula presented) in agreement with photoemission spectra and tunneling current measurements which is found to significantly affect the localization and hybridization characteristics as well as the three-dimensional spatial distribution of quasiparticle states and thus constitutes the central feature of the model. The formation of the pseudogap is rationalized via a repulsion between occupied and unoccupied conduction band quasiparticle states induced by antiferromagnetic correlations occurring on length scales which—for the most relevant parameters—are controlled by the doping-dependent tight-binding Fermi surface. Light is shed on experimental results which hitherto have not found a satisfactory rationalization. © 1999 The American Physical Society.

Abstract:

We discuss the dynamics of a single hole in t-J model at finite temperature, in the limit of large spatial dimensions. The problem is shown to yield a simple and physically transparent solution, that exemplifies the continuous thermal evolution of the underlying string picture from the T = 0 string-pinned limit through to the paramagnetic phase.

Abstract:

A theory is developed for the single-particle spectra of the symmetric Anderson model, in which local moments are introduced explicitly from the outset. Dynamical coupling of single-particle processes to low-energy spin-flip excitations leads, within the framework of a two-self-energy description, to a theory in which both low- and high-energy spectral features are simultaneously captured, while correctly preserving Fermi liquid behaviour at low energies. The atomic limit, non-interacting limit and strong-coupling behaviour of the spectrum are each recovered. For strong coupling in particular, both the exponential asymptotics of the Kondo resonance and concomitant many-body broadening of the Hubbard satellite bands are shown to arise naturally within the present approach.

Abstract:

We study the magnetic properties of a site-disordered Anderson-Hubbard model at half-filling on a simple cubic lattice, via a mapping of its low-frequency transverse spin excitations onto those of an effective underlying Heisenberg model with self-consistently determined exchange couplings. Exact in the strong-coupling limit, the mapping remains accurate over the dominant region of the phase plane where the ground state is a disordered antiferromagnet. The effect of disorder and interaction strength on the resultant exchange couplings is examined in detail, and rationalized microscopically. Frustration is found to occur, even within the antiferromagnetic phase, although the ground state is shown to be stable with respect to zero-point quantum spin fluctuations. To probe finite-temperature magnetic properties, an Onsager reaction-field approach to the effective Heisenberg model in the paramagnetic phase is employed. We focus on the effect of disorder on the Néel temperature and the nature of the thermal transition to the ordered phase.