A. Zawadowski

Exotic Kondo effects in metals : magnetic ions in a crystalline electric field and tunnelling centres

The ordinary single-channel Kondo model consists of one or more spin-½ local moments interacting antiferromagnetically with conduction electrons in a metal. This model has provided a paradigm for understanding many phenomena of strongly correlated electronic materials, ranging from the formation of heavyfermion Fermi liquids to the mapping of a one-band model in the cuprate superconductors. The simplest extension of this ordinary Kondo model in metals which yields exotic non-Fermi-liquid physics is the multichannel Kondo impurity model in which the conduction electrons are given an extra quantum label known as the channel or flavour index. In the overcompensated regime of this model, nonFermi-liquid physics is possible, in contrast with the single-channel model. We overview here the multichannel Kondo impurity model candidates most extensively studied for explaining real materials, specifically the two-level system Kondo model relevant for metallic glasses, nanoscale devices and some doped semiconductors,...

Magnetic impurities in non-magnetic metals

The properties of 3d transition metal impurities in simple metal hosts are summarized. There is a short discussion of the basic microscopic models, then the Anderson model is treated in some detail. The next section considers the s-d model and the Kondo effect. The main experimental features are reviewed and finally the question of dilute alloys is considered.

Theory of the fano resonance in the STM tunneling density of states due to a single kondo impurity

The conduction electron density of states nearby single magnetic impurities, as measured recently by scanning tunneling microscopy (STM), is calculated, taking into account tunneling into conduction electron states only. The Kondo effect induces a narrow Fano resonance in the conduction electron density of states. The line shape varies with the distance between STM tip and impurity, in qualitative agreement with experiments, but is very sensitive to details of the band structure. For a Co impurity the experimentally observed width and shift of the Kondo resonance are in accordance with those obtained from a combination of band structure and strongly correlated calculations.

Scaling and the renormalization group in the kondo effect

Abstract Applying renormalization group techniques, scaling laws in terms of the invariant exchange coupling are derived for the Kondo effect. The effective energy dependent coupling strength goes to unity at small energies. This medium strong invariant coupling is the likely origin of the difficulties in working out the low temperature Kondo scattering, and is the reason why comparison between low temperature experimental results and the predictions of the standard theories is not very meaningful.

DEPHASING IN METALS BY TWO-LEVEL SYSTEMS IN THE 2-CHANNEL KONDO REGIME

We point out a novel, non-universal contribution to the dephasing rate 1/\tau_\phi \equiv \gamma_\phi of conduction electrons in metallic systems: scattering off non-magnetic two-level systems (TLSs) having almost degenerate Kondo ground states. In the regime \Delta_{ren} < T < T_K (\Delta_{ren} = renormalized level splitting, T_K = Kondo temperature), such TLSs exhibit non-Fermi-liquid physics that can cause \gamma_\phi, which generally decreases with decreasing T, to seemingly saturate in a limited temperature range before vanishing for T \to 0. This could explain the saturation of dephasing recently observed in gold wires [Mohanty et al. Phys. Rev. Lett. 78, 3366 (1997)].

Charge-transfer fluctuation, d-wave superconductivity, and the B1g Raman phonon in cuprates

The Raman spectrum of the

Kondo effect and dephasing in low-dimensional metallic systems

B_{1g}

Multiband electronic Raman scattering in bilayer superconductors.

phonon in the superconducting cuprate materials is investigated theoretically in detail in both the normal and superconducting phases, and is contrasted with that of the

Physical origin of the buckling in CuO2: Electron-phonon coupling and Raman spectra

A_{1g}

Partial cancellation in the electron-hole and electron-electron correlation in the symmetric anderson model

phonon. A mechanism involving the charge transfer fluctuation between the two oxygen ions in the CuO