Direct experimental verification of applicability of single-site model for angle integrated photoemission of small TKT_{K} concentrated Ce compounds

Bulk-sensitive high-resolution Ce 4f spectra have been obtained from 3d $\to$ 4f resonance photoemission measurements on La$_{1-x}$Ce$_x$Al$_2$ and La$_{1-x}$Ce$_x$Ru$_2$ for $x = 0.0, 0.04, 1.0$. The 4f spectra of low-Kondo-temperature ($T_{K}$) (La,Ce)Al$_2$ are essentially identical except for a slight increase of the Kondo peak with $x$, which is consistent with a known increase of $T_{K}$ with $x$. In contrast, the 4f spectra of high-$T_{K}$ (La,Ce)Ru$_2$ show a Kondo-like peak and also a 0.5 eV structure which increases strongly with $x$. The resonance photon-energy dependences of the two contributions are different and the origin of the 0.5 eV structure is still uncertain.Comment: submitted to SCES 2001, two-columnn format, modified tex

Local Non-Fermi Liquid Theory of Magnetic Impurity Effects in Carbon Nanotubes

Magnetic impurity effects in carbon nanotubes are studied theoretically. The multi channel Kondo effect is investigated with the band structure of the metallic nanotubes. The local non-Fermi liquid behavior is realized at temperatures lower than the Kondo temperature T_K. The density of states of localized electron has a singularity |omega|^1/2 which gives rise to a pseudo gap at the Kondo resonance in low temperatures. The temperature dependence of the electronic resistivity is predicted as T^1/2, and the imaginary part of dynamical susceptibilities has the |omega|^1/2 dependence.Comment: 3 page

Similar temperature scale for valence changes in Kondo lattices with different Kondo temperatures

The Kondo model predicts that both the valence at low temperatures and its temperature dependence scale with the characteristic energy T_K of the Kondo interaction. Here, we study the evolution of the 4f occupancy with temperature in a series of Yb Kondo lattices using resonant X-ray emission spectroscopy. In agreement with simple theoretical models, we observe a scaling between the valence at low temperature and T_K obtained from thermodynamic measurements. In contrast, the temperature scale T_v at which the valence increases with temperature is almost the same in all investigated materials while the Kondo temperatures differ by almost four orders of magnitude. This observation is in remarkable contradiction to both naive expectation and precise theoretical predictions of the Kondo model, asking for further theoretical work in order to explain our findings. Our data exclude the presence of a quantum critical valence transition in YbRh2Si2

Single Impurity Anderson Model with Coulomb Repulsion between Conduction Electrons on the Nearest-Neighbour Ligand Orbital

We study how the Kondo effect is affected by the Coulomb interaction between conduction electrons on the basis of a simplified model. The single impurity Anderson model is extended to include the Coulomb interaction on the nearest-neighbour ligand orbital. The excitation spectra are calculated using the numerical renormalization group method. The effective bandwidth on the ligand orbital, $D^{eff}$, is defined to classify the state. This quantity decreases as the Coulomb interaction increases. In the $D^{eff} > \Delta$ region, the low energy properties are described by the Kondo state, where $\Delta$ is the hybridization width. As $D^{eff}$ decreases in this region, the Kondo temperature $T_{K}$ is enhanced, and its magnitude becomes comparable to $\Delta$ for $D^{eff} \sim \Delta$. In the $D^{eff} < \Delta$ region, the local singlet state between the electrons on the $f$ and ligand orbitals is formed.Comment: 5 pages, 3 figures, LaTeX, to be published in J. Phys. Soc. Jpn Vol. 67 No.

Intersite coupling effects in a Kondo lattice

The La dilution of the Kondo lattice CeCoIn_5 is studied. The scaling laws found for the magnetic susceptibility and the specific heat reveal two well-separated energy scales, corresponding to the single impurity Kondo temperature T_K and an intersite spin-liquid temperature T^*. The Ce-dilute alloy has the expected Fermi liquid ground state, while the specific heat and resistivity in the dense Kondo regime exhibit non-Fermi-liquid behavior, which scales with T^*. These observations indicate that the screening of the magnetic moments in the lattice involves antiferromagnetic intersite correlations with a larger energy scale in comparison with the Kondo impurity case.Comment: 4 pages, 4 figure

Interaction Effect in the Kondo Energy of the Periodic Anderson-Hubbard Model

We extend the periodic Anderson model by switching on a Hubbard $U_d$ for the conduction electrons. The nearly integral valent (Kondo) limit of the Anderson--Hubbard model is studied with the Gutzwiller variational method. The new formula for the Kondo energy contains the $U_d$-dependent chemical potential of the Hubbard subsystem in the exponent, and the correlation-induced band narrowing in the prefactor. Both effects tend to suppress the Kondo scale, which can be understood to result from the blocking of hybridization (this behaviour is the opposite of that found for Kondo--Hubbard models). At half-filling, we find a Brinkman--Rice-type transition which leads from a small-gap Kondo insulator to a Mott insulator.Comment: 4 pages (ReVTeX), submitted for publicatio

Room temperature spin Kondo effect and intermixing in Co/Cu non-local spin valves

The anomalous low temperature suppression of the spin accumulation signalDRNLin non-localspin valves (NLSVs) based on common ferromagnet (FM)/normal metal (N) pairings has recentlybeen shown to result from a manifestation of the Kondo effect. Local magnetic moments in the Ndue to even minor levels of FM/N interdiffusion depolarize the injected spin current, suppressingthe effective spin polarization around and below the Kondo temperatureTK. Previous studies havefocused on FM/N combinations that happen to have lowTKso that Kondo effects occur only wellbelow 300 K. Here, we study NLSVs based on Co/Cu, a materials combination that is not onlytechnologically relevant but also has a highTK, up to 500 K. Despite the negligibleequilibriumsol-ubility of Co in Cu, we find clear Kondo effects in bothDRNLand Cu resistivity, due to Co/Cuintermixing that we probeviaquantitative transmission electron microscopy. Most significantly,under certain conditions the spin Kondo effect suppresses the injected spin polarizationeven atroom temperature, with important technological implications. Studies as a function of the Cu thick-ness and annealing temperature reveal complex trends in interdiffusion lengths and Kondo effects,which we interpret in terms of the interplay between diffusion kinetics and thermodynamics, aswell as the thickness dependence of the Kondo effect

Shape evolution of electrodeposited bumps into deep cavities

Metal posts and finer pitch solder bumps are the indispensable microconnectors for chip size packaging and are formed by electrodeposition into deep cavities. It is difficult to stir inside these deep cavities. Natural convection due to density difference is effective in stirring inside cavity with 200 mum cathode width of aspect ratio of one. The bump shape increases toward lower side in a vertical cathode arrangement with placement angle of Theta = 90 degrees. This increase in bump height results from a collision of flow along the lower side of the resist sidewall which enlarges local current and thickens the lower edge of bumps. The effect of natural convection is also evident in the neighboring two cavities of 200 mum cathode width. The natural convection is not effective for cavities with less than 100 mum cathode width. The bump shapes become flat. Only diffusion occurs within these smaller than 100 mum cavities. (C) 2001 The Electrochemical Society. All rights reserved.</p