P. Schlottmann

Some exact results for dilute mixed-valent and heavy-fermion systems

Abstract Numerous exact results for magnetic impurities in simple metals have been obtained during the last eight years. These systems exhibit a variety of unusual low-temperature properties attributed to highly correlated electronic states, e.g. a mixed valence and large electronic contributions to the specific heat and the magnetic susceptibility. Some of these exact results obtained by means of the generalized Bethe Ansatz are reviewed here. Special emphasis is given to the solution of the degenerate Anderson model, in particular in the presence of mechanisms lifting the degeneracy of the f-level, e.g. crystalline fields, spin-orbit coupling and the magnetic field. This focus makes the present article complementary to the previous ones by Andrei, Furuya and Lowenstein and by Tsvelick and Wiegmann. Comparisons between theory and experiments are also reviewed.

On the longitudinal static and dynamic susceptibility of spin-1/2 Kondo systems

The impurity spin polarization, static susceptibility, and longitudinal impurity spin relaxation rate are calculated for thes-d model as function of temperature and magnetic field for ferromagnetic and antiferromagnetic exchange coupling. The thermodynamic functions and the dynamical susceptibility are obtained from the impurity relaxation spectrum, which is approximated by taking into account the infrared-like singularities. For antiferromagnetic coupling the zero-field susceptibility obeys a Curie-Weiss law1/χ∼4.6(T+θ) for high and intermediate temperatures and it approaches the finite value1/χ∼3.8θ for zero temperature. The zero-field relaxation rate is much larger than the Korringa value; it decreases with temperature and approaches the nonzero value1/T1∼1.2θ for zero temperature. The relaxation rate decreases with increasing field. The results for the spin polarization agree well with the experimental data for the Cu:Fe alloy.

Exact Results for Highly Correlated Electron Systems in One Dimension

One-dimensional conductors are a long-standing topic of research with direct applications to organic conductors and mesoscopic rings. The discovery of the ceramic high-temperature superconductors has revitalized the interest in low-dimensional charge and spin fluctuations of highly correlated electron systems. Several mechanisms proposed to explain the high-Tc superconductors invoke properties of the two-dimensional Hubbard model, but probably also some one-dimensional aspects are relevant. Numerous one-dimensional models for correlated electrons have been studied with various approximate, asymptotically exact and exact methods. These results lead to the concept of Luttinger liquid for interacting electron gases without excitation gaps (metallic systems). Characteristic of Luttinger liquids are the charge and spin separation, marginal Fermi liquid properties, e.g. the absence of quasiparticles in the vicinity of the Fermi surface, nonuniversal power-law singularities in the one-particle spectral function and the related absence of a discontinuity in the momentum distribution at the Fermi level, the power-law decay of correlation functions for long times and large distances, persistent currents in finite rings, etc. Due to the peculiarities of the phase space in one dimension some of the models have sufficient conserved currents to be completely integrable. We review exact results derived within the framework of Bethes ansatz for integrable one-dimensional models of correlated electrons. The Bethe-ansatz method is presented by explicitly showing the steps leading to the solution of the N-component electron gas interacting via a δ-function potential (repulsive and attractive interaction), which is probably the simplest model of correlated electrons. Emphasis is given to the procedure to extract the groundstate properties, the classification of states, the excitation spectrum, the thermodynamics and finite size effects, such as critical exponents of correlation functions and persistent currents. The method is then applied to numerous other models, e.g. (i) a two-band model involving attractive and repulsive potentials and crystalline fields splitting the bands, (ii) the traditional Hubbard chain with attractive and repulsive U, (iii) the degenerate Hubbard model with repulsive U, which displays a metal–insulator transition at a finite U, (iv) a two-band Hubbard model with repulsive U, (v) the traditional supersymmetric t–J model (vi) a two-band supersymmetric t–J model with band-splitting and (vii) the N-component supersymmetric t–J model. Finally, results for models with long-range interactions, in particular r-2 and sinh-2(r) potentials, are briefly reviewed.

Lattice-driven magnetoresistivity and metal-insulator transition in single-layered iridates

Sr

Multichannel Kondo problem and some applications

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The quadrupolar kondo effect: Lattice instability and large γ-values

IrO

Intersite coupling effects in a kondo lattice.

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d-Hole localization and the suppression of superconductivity in YBa2(Cu1-xZnx)3O7−y

exhibits an insulating state driven by spin-orbit interactions. We report two phenomena, namely, a large magnetoresistivity in Sr

Tuning the J eff = 1 2 insulating state via electron doping and pressure in the double-layered iridate Sr 3 Ir 2 O 7

{}_{2}

Non-Fermi-liquid behavior in nearly ferromagnetic SrIrO3 single crystals

IrO