133 research outputs found
Metallic Ferromagnetism in the Kondo Lattice
Metallic magnetism is both ancient and modern, occurring in such familiar
settings as the lodestone in compass needles and the hard drive in computers.
Surprisingly, a rigorous theoretical basis for metallic ferromagnetism is still
largely missing. The Stoner approach perturbatively treates Coulomb
interactions when the latter need to be large, while the Nagaoka approach
incorporates thermodynamically negligible electrons into a half-filled band.
Here, we show that the ferromagnetic order of the Kondo lattice is amenable to
an asymptotically exact analysis over a range of interaction parameters. In
this ferromagnetic phase, the conduction electrons and local moments are
strongly coupled but the Fermi surface does not enclose the latter (i.e. it is
small). Moreover, non-Fermi liquid behavior appears over a range of frequencies
and temperatures. Our results provide the basis to understand some
long-standing puzzles in the ferromagnetic heavy fermion metals, and raises the
prospect for a new class of ferromagnetic quantum phase transitions.Comment: 21 pages, 9 figures, including Supporting Informatio
Multichannel pseudogap Kondo model: Large-N solution and quantum-critical dynamics
We discuss a multichannel SU(N) Kondo model which displays non-trivial
zero-temperature phase transitions due to a conduction electron density of
states vanishing with a power law at the Fermi level. In a particular large-N
limit, the system is described by coupled integral equations corresponding to a
dynamic saddle point. We exactly determine the universal low-energy behavior of
spectral densities at the scale-invariant fixed points, obtain anomalous
exponents, and compute scaling functions describing the crossover near the
quantum-critical points. We argue that our findings are relevant to recent
experiments on impurity-doped d-wave superconductors.Comment: 4 pages, 3 figs; extended discussion of large-N spin representations,
added references; accepted for publication in PR
Differential expression of DNA topoisomerase II alpha and -beta in P-gp and MRP-negative VM26, mAMSA and mitoxantrone-resistant sublines of the human SCLC cell line GLC4.
Sublines of the human small-cell lung carcinoma (SCLC) cell line GLC4 with acquired resistance to teniposide, amsacrine and mitoxantrone (GLC4/VM20x, GLC4/AM3x and GLC4/MIT60x, respectively) were derived to study the contribution of DNA topoisomerase II alpha and -beta (TopoII alpha and -beta) to resistance for TopoII-targeting drugs. The cell lines did not overexpress P-glycoprotein or the multidrug resistance-associated protein but were cross-resistant to other TopoII drugs. GLC4/VM20x showed a major decrease in TopoII alpha protein (54%; for all assays presented in this paper the GLC4 level was defined to be 100%) without reduction in TopoII beta protein; GLC4/AM3x showed only a major decrease in TopoII beta protein (to 18%) and not in TopoII alpha. In GLC4/MIT60x, the TopoII alpha and -beta protein levels were both decreased (TopoII alpha to 31%; TopoII beta protein was undetectable). The decrease in TopoII alpha protein in GLC4/VM20x and GLC4/MIT60x, was mediated by decreased TopoII alpha mRNA levels. Loss of TopoII alpha gene copies contributed to the mRNA decrease in these cell lines. Only in the GLC4/MIT60x cell line was an accumulation defect observed for the drug against which the cell line was made resistant. In conclusion, TopoII alpha and -beta levels were decreased differentially in the resistant cell lines, suggesting that resistance to these drugs may be mediated by a decrease in a specific isozyme
Non Fermi Liquid Behaviour near a spin-glass transition
In this paper we study the competition between the Kondo effect and RKKY
interactions near the zero-temperature quantum critical point of an Ising-like
metallic spin-glass. We consider the mean-field behaviour of various physical
quantities. In the `quantum- critical regime' non-analytic corrections to the
Fermi liquid behaviour are found for the specific heat and uniform static
susceptibility, while the resistivity and NMR relaxation rate have a non-Fermi
liquid dependence on temperature.Comment: 15 pages, RevTex 3.0, 1 uuencoded ps. figure at the en
Characterization of BIS20x3, a bi-specific antibody activating and retargeting T-cells to CD20-positive B-cells
This paper describes a bi-specific antibody, which was called BIS20x3. It retargets CD3ɛ-positive cells (T-cells) to CD20-positive cells and was obtained by hybrid–hybridoma fusion. BIS20x3 could be isolated readily from quadroma culture supernatant and retained all the signalling characteristics associated with both of its chains. Cross-linking of BIS20x3 on Ramos cells leads to DNA fragmentation percentages similar to those obtained after Rituximab-cross-linking. Cross-linking of BIS20x3 on T-cells using cross-linking F(ab′)2-fragments induced T-cell activation. Indirect cross-linking of T-cell-bound BIS20x3 via Ramos cells hyper-activated the T-cells. Furthermore, it was demonstrated that BIS20x3 effectively re-targets T-cells to B-cells, leading to high B-cell cytotoxicity. The results presented in this paper show that BIS20x3 is fully functional in retargeting T-cells to B-cells and suggest that B-cell lymphomas may represent ideal targets for T-cell retargeting bi-specific antibodies, because the retargeted T-cell is maximally stimulated in the presence of B-cells. Additionally, since B-cells may up-regulate CD95/ Fas expression upon binding of CD20-directed antibodies, B-cells will become even more sensitive for T-cell mediated killing via CD95L/ Fas L, and therefore supports the intention to use T-cell retargeting bi-specific antibodies recognizing CD20 on B-cell malignancies as a treatment modality for these diseases. © 2001 Cancer Research Campaign http://www.bjcancer.co
Bethe ansatz approach to thermodynamics of superconducting magnetic alloys
We derive thermodynamic Bethe ansatz equations for a model describing an
Anderson impurity embedded in a BCS superconductor. The equations
are solved analytically in the zero-temperature limit, T=0. It is shown that
the impurities depress superconductivity in the Kondo limit, however at T=0 the
system remains in the superconducting state for any impurity concentration. In
the mixed-valence regime, an impurity contribution to the density of states of
the system near the Fermi level overcompensates a Cooper pairs weakening, and
superconductivity is enhanced.Comment: 4 pages, RevTex, to appear in PR
Critical properties of the Fermi-Bose Kondo and pseudogap Kondo models: Renormalized perturbation theory
Magnetic impurities coupled to both fermionic and bosonic baths or to a
fermionic bath with pseudogap density of states, described by the Fermi-Bose
Kondo and pseudogap Kondo models, display non-trivial intermediate coupling
fixed points associated with critical local-moment fluctuations and local
non-Fermi liquid behavior. Based on renormalization group together with a
renormalized perturbation expansion around the free-impurity limit, we
calculate various impurity properties in the vicinity of those
intermediate-coupling fixed points. In particular, we compute the conduction
electron T matrix, the impurity susceptibility, and the residual impurity
entropy, and relate our findings to certain scenarios of local quantum
criticality in strongly correlated lattice models.Comment: 16 pages, 5 figs; (v2) large-N results for entropy of Bose-Kondo
model added; (v3) final version as publishe
Low Temperature Properties of Anisotropic Superconductors with Kondo Impurities
We present a self-consistent theory of superconductors in the presence of
Kondo impurities, using large- slave-boson methods to treat the impurity
dynamics. The technique is tested on the s-wave case and shown to give good
results compared to other methods for . We calculate low temperature
thermodynamic and transport properties for various superconducting states,
including isotropic s-wave and representative anisotropic model states with
line and point nodes on the Fermi surface.Comment: 21 pages, RevTeX 3.0, 12 figures available upon request, UF preprin
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