Large-N limit of a magnetic impurity in unconventional density waves

We investigate the effect of unconventional density wave (UDW) condensate on an Anderson impurity using large-N technique at T=0. In accordance with previous treatments of a Kondo impurity in pseudogap phases, we find that Kondo effect occurs only in a certain range of parameters. The f-electron density of states reflects the influence of UDW at low energies and around the maximum of the density wave gap. The static spin susceptibility diverges at the critical coupling, indicating the transition from strong to weak coupling. In the dynamic spin susceptibility an additional peak appears showing the presence the UDW gap. Predictions concerning non-linear density of states are made. Our results apply to other unconventional condensates such as d-wave superconductors and d-density waves as well.Comment: 9 pages, 7 figure

Ground State Properties of Anderson Impurity in a Gapless Host

Using the Bethe ansatz method, we study the ground state properties of a $U\to\infty$ Anderson impurity in a ``gapless'' host, where a density of band states vanishes at the Fermi level $\epsilon_F$ as $|\epsilon-\epsilon_F|$. As in metals, the impurity spin is proven to be screened at arbitrary parameters of the system. However, the impurity occupancy as a function of the bare impurity energy is shown to acquire novel qualitative features which demonstrate a nonuniversal behavior of the system. The latter explains why the Kondo screening is absent (or exists only at quite a large electron-impurity coupling) in earlier studies based on scaling arguments.Comment: 5 pages, no figure, RevTe

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

Critical local-moment fluctuations, anomalous exponents, and omega/T scaling in the Kondo problem with a pseudogap

Experiments in heavy-fermion metals and related theoretical work suggest that critical local-moment fluctuations can play an important role near a zero-temperature phase transition. We study such fluctuations at the quantum critical point of a Kondo impurity model in which the density of band states vanishes as |E|^r at the Fermi energy (E = 0). The local spin response is described by a set of critical exponents that vary continuously with r. For 0 < r < 1, the dynamical susceptibility exhibits omega/T scaling with a fractional exponent, implying that the critical point is interacting.Comment: 4 pages, 3 figures; enhanced figures, expanded discussion of small-r expansio

Prussian blue onto activated carbon as a catalyst for heterogeneous fenton-like processes.

The main goal of this contribution is the development of a new heterogeneous Fenton-like oxidation system based on Prussian Blue supported over a commercially available granular activated carbon (GAC). The catalysts were prepared following basically three different approaches: (i) Prussian Blue (Fe3[Fe(CN)6]2) particles adsorbed onto the GAC by impregnation, (ii) Prussian Blue nanoparticles (PBNP) prepared ex-situ and adsorbed onto the GAC; and (iii) PBNP prepared in-situ onto the GAC. The catalysts were characterized by SEM, EDS, BET surface area and Fe content. Their performance in the catalytic wet peroxide oxidation of a model azo dye, Orange G, was tested in a batch lab-scale stirred reactor. Activity and stability runs were carried out and analyzed in terms of dye discoloration, Total Organic Carbon removal, UV-vis spectra and degree of iron leaching.Fil: Doumic, Lucila Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; ArgentinaFil: Salierno, Gabriel Leonardo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Cassanello, Miryan C.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Haure, Patricia Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; ArgentinaFil: Ayude, María Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingenieria; Argentin

Kondo effect in a quantum critical ferromagnet

We study the Heisenberg ferromagnetic spin chain coupled with a boundary impurity. Via Bethe ansatz solution, it is found that (i) for J>0, the impurity spin behaves as a diamagnetic center and is completely screened by 2S bulk spins in the ground state, no matter how large the impurity spin is; (ii) The specific heat of the local composite (impurity plus 2S bulk spins which form bound state with it) shows a simple power law $C_{loc}\sim T^{3/2}$. (iii)For J<0, the impurity is locked into the critical behavior of the bulk. Possible phenomena in higher dimensions are discussed.Comment: 6page Revtex, no figure, final version in PRB, Jun 1 issue, 199

Kondo screening in d-wave superconductors in a Zeeman field and implications for STM spectra of Zn-doped cuprates

We consider the screening of an impurity moment in a d-wave superconductor under the influence of a Zeeman magnetic field. Using the Numerical Renormalization Group technique, we investigate the resulting pseudogap Kondo problem, in particular the field-induced crossover behavior in the vicinity of the zero-field boundary quantum phase transition. The impurity spectral function and the resulting changes in the local host density of states are calculated, giving specific predictions for high-field STM measurements on impurity-doped cuprates.Comment: 5 pages, 4 figs, (v2) remark on c-axis field added, discussion extended, (v3) final version as publishe

Absence of overscreened Kondo effect in ferromagnetic host

We study the low temperature behavior of a boundary magnetic impurity S'=1/2 in an open ferromagnetic Takhatajian-Babujian spin-S chain. For antiferromagnetic Kondo coupling, it is show via Bethe ansatz solution that the impurity spin is always locked into the critical behavior the bulk. At low temperature, a local composite of spin S-1/2 forms near the impurity site and its contribution to specific heat is of simple power law T^{1/2}. The absence of overscreened Kondo effect is due to the large correlation length of host spins which is divergent near the quantum critical point.Comment: 4 pages. to appear in Phys. Rev. B1(R4A)(2000

Localization of quasiparticles in a disordered vortex

We study the diffusive motion of low-energy normal quasiparticles along the core of a single vortex in a dirty, type-II, s-wave superconductor. The physics of this system is argued to be described by a one-dimensional supersymmetric nonlinear sigma model, which differs from the sigma models known for disordered metallic wires. For an isolated vortex and quasiparticle energies less than the Thouless energy, we recover the spectral correlations that are predicted by random matrix theory for the universality class C. We then consider the transport problem of transmission of quasiparticles through a vortex connected to particle reservoirs at both ends. The transmittance at zero energy exhibits a weak localization correction reminiscent of quasi-one-dimensional metallic systems with symmetry index beta = 1. Weak localization disappears with increasing energy over a scale set by the Thouless energy. This crossover should be observable in measurements of the longitudinal heat conductivity of an ensemble of vortices under mesoscopic conditions. In the regime of strong localization, the localization length is shown to decrease by a factor of 8 as the quasiparticle energy goes to zero.Comment: 38 pages, LaTeX2e + epsf, 4 eps figures, one reference adde