Realization of Strong Coupling Fixed Point in Multilevel Kondo Models

Impurity four- and six-level Kondo model, in which an ion is tunneling among four- and six-stable points and interacting with surrounding conduction electrons, are investigated by using the perturbative and numerical renormalization group methods. It is shown that purely orbital Kondo effects occur at low temperatures in these systems which are direct generalizations of the Kondo effect in the so-called two-level system. This result offers a good explanation for the enhanced and magnetically robust Sommerfeld coefficient observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published in Journal of Physical Society Japan supplemen

Theory of spin-polarized transport in semiconductor heterojunctions: Proposal for spin injection and detection in silicon

Spin injection and detection in silicon is a difficult problem, in part because the weak spin-orbit coupling and indirect gap preclude using standard optical techniques. We propose two ways to overcome this difficulty, and illustrate their operation by developing a model for spin-polarized transport across a heterojunction. We find that equilibrium spin polarization of holes leads to a strong modification of the spin and charge dynamics of electrons, and we show how the symmetry properties of the charge current can be exploited to detect spin injection in silicon using currently available techniques.Comment: 4 pages, 4 figures, added footnot

Relativistic jet models for the BL Lacertae object Mrk 421 during three epochs of observation

Coordinated observation of the nearby BL Lacertae object Mrk 421 obtained during May 1980, January 1984, and March 1984 are described. These observations give a time-frozen picture of the continuous spectrum of Mrk 421 at X-ray, ultraviolet, optical, and radio wavelengths. The observed spectra have been fitted to an inhomogeneous relativistic jet model. In general, the models reproduce the data well. Many of the observed differences during the three epochs can be attributed to variations in the opening angle of the jet and in the angle that the jet makes to the line of sight. The jet models obtained here are compared with the homogeneous, spherically symmetric, synchrotron self-Compton models for this source. The models are also compared with the relativistic jet models obtained for other active galactic nuclei

A formulation of the Yang-Mills theory as a deformation of a topological field theory based on background field method and quark confinement problem

By making use of the background field method, we derive a novel reformulation of the Yang-Mills theory which was proposed recently by the author to derive quark confinement in QCD. This reformulation identifies the Yang-Mills theory with a deformation of a topological quantum field theory. The relevant background is given by the topologically non-trivial field configuration, especially, the topological soliton which can be identified with the magnetic monopole current in four dimensions. We argue that the gauge fixing term becomes dynamical and that the gluon mass generation takes place by a spontaneous breakdown of the hidden supersymmetry caused by the dimensional reduction. We also propose a numerical simulation to confirm the validity of the scheme we have proposed. Finally we point out that the gauge fixing part may have a geometric meaning from the viewpoint of global topology where the magnetic monopole solution represents the critical point of a Morse function in the space of field configurations.Comment: 45 pages, 3 figures included in LaTe

Superconductivity in Organic Compounds with Pseudo-Triangular Lattice

We study spin fluctuation (SF) mediated superconductivity (SC) in a half-filled square lattice Hubbard model with the transfer matrices -t between nearest neighbor sites and -t' between a half of next nearest neighbor sites neighboring along only one of the directions, considering application of this model to organic kappa-(BEDT-TTF)2X compounds. Varying the t'/t value from 0 to 1, one can interpolate between a square and an equilateral triangular lattice, the latter giving frustration to antiferromagnetically (AF) coupled spin systems. Within the fluctuation exchange (FLEX) approximation, we calculate chi(q,omega), Tc and the SC order parameter for various model parameter values and find that both AF and SC are suppressed as one approaches the frustration geometry or |(t'/t)-1| \to 0. The SC phase, however, extends beyond the AF phase boundary fairly close to t'/t=1 for realistic U/t values. The order parameter is of x2-y2-type for t'/t1.Comment: 4 pages, 5 eps figures, to appear in J. Phys. Soc. Jp

An Electronic Model for CoO2CoO_2 layer based systems: Chiral RVB metal and Superconductivity

Takada et al. have reported superconductivity in layered Na__x CoO_2.yH_2O ($T_c \approx5 K$) and more recently Wen et al. in $A_xCoO_{2+\delta}$ ($A = Na,K$)(\tc$\approx~31 K$). We model a reference neutral \cob layer as an orbitally non-degenerate spin-\half antiferromagnetic Mott insulator on a triangular lattice and Na__x CoO_2.yH_2O and $A_xCoO_{2+\delta}$ as electron doped Mott insulators described by a t-J model. It is suggested that at optimal doping chiral spin fluctuations enhanced by the dopant dynamics leads to a d-wave superconducting state. A chiral RVB metal, a PT violating state with condensed RVB gauge fields, with a possible weak ferromagnetism and low temperature p-wave superconductivity are also suggested at higher dopings.Comment: 4 pages of LaTex file, 6 figures in eps files. Typos and minor corrections mad

Renormalizing a BRST-invariant composite operator of mass dimension 2 in Yang-Mills theory

We discuss the renormalization of a BRST and anti-BRST invariant composite operator of mass dimension 2 in Yang-Mills theory with the general BRST and anti-BRST invariant gauge fixing term of the Lorentz type. The interest of this study stems from a recent claim that the non-vanishing vacuum condensate of the composite operator in question can be an origin of mass gap and quark confinement in any manifestly covariant gauge, as proposed by one of the authors. First, we obtain the renormalization group flow of the Yang-Mills theory. Next, we show the multiplicative renormalizability of the composite operator and that the BRST and anti-BRST invariance of the bare composite operator is preserved under the renormalization. Third, we perform the operator product expansion of the gluon and ghost propagators and obtain the Wilson coefficient corresponding to the vacuum condensate of mass dimension 2. Finally, we discuss the connection of this work with the previous works and argue the physical implications of the obtained results.Comment: 49 pages, 35 eps-files, A number of typographic errors are corrected. A paragraph is added in the beginning of section 5.3. Two equations (7.1) and (7.2) are added. A version to be published in Phys. Rev.