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We find a mixed chirality $d$-wave superconducting state in the coexistence region between antiferromagnetism and interaction-driven superconductivity in lightly doped honeycomb materials. This state has a topological chiral $d+id$-wave symmetry in one Dirac valley but $d-id$-wave symmetry in the other valley and hosts two counter-propagating edge states, protected in the absence of intervalley scattering. A first-order topological phase transition, with no bulk gap closing, separates the chiral $d$-wave state at small magnetic moments from the mixed chirality $d$-wave phase., Comment: 5 pages, 3 figures. v3: updated Fig. 2, published version

We theoretically investigate the non-equilibrium current through a quantum dot coupled to one- dimensional electron leads, utilizing a controlled frequency-dependent renormalization group (RG) approach. We compute the non-equilibrium conductance for large bias voltages and address the interplay between decoherence, Kondo entanglement and Luttinger physics. The combined effect of large bias voltage and strong interactions in the leads, known to stabilize two-channel Kondo physics, leads to non-trivial modifications of the conductance. For weak interactions, we build an analogy to a dot coupled to helical edge states of two-dimensional topological insulators., Comment: 4 pages, 4 figures

We present low temperature magnetoresistance measurements of Ar-irradiated SrTiO3 under an applied electrostatic field. The electric field, applied through a back gate bias, modulates both the mobility and sheet density, with a greater effect on the former. For high mobilities, 3-dimensional orbital magnetoresistance is observed. For low mobilities, negative magnetoresistance that is consistent with the suppression of 2-dimensional weak-localization is observed. The crossover from 3 to 2-dimensional transport arises from a modulation in the carrier confinement, which is enhanced by the electric field dependent dielectric constant of SrTiO3. The implications of our results on the development of oxide electronic devices will be discussed., Comment: 4 pages, 5 figures

We study shot noise in the current of quantum dots whose low-energy behaviour corresponds to an SU(N) Kondo model, focusing on the case N=4 relevant to carbon nanotube dots. For general N, two-particle Fermi liquid interactions have two distinct effects: they can enhance the noise via back-scattering processes with an N-dependent effective charge, and can also modify the coherent partition noise already present without interactions. For N=4, in contrast to the SU(2) case, interactions enhance shot noise solely through an enhancement of partition noise. This leads to a non-trivial prediction for experiment., Comment: 4+ pages; error in numerical prefactor describing interaction effect on noise corrected

We investigate a mesoscopic setup composed of a small electron droplet (dot) coupled to a larger quantum dot (grain) also subject to Coulomb blockade as well as two macroscopic leads used as source and drain. An exotic Kondo ground state other than the standard SU(2) Fermi liquid unambiguously emerges: an SU(4) Kondo correlated liquid. The transport properties through the small dot are analyzed for this regime, through boundary conformal field theory, and allow a clear distinction with other regimes such as a two-channel spin state or a two-channel orbital state., Comment: 13 pages, 3 figures

We investigate the transport properties of a (small) quantum dot connected to Fermi liquid leads with a power-law density of states (DOS). Such a system, if experimentally realizable, will have interesting physical properties including: (i) non-saturating Coulomb blockade peak widths; (ii) a non-unitary Kondo peak symmetrically placed between the Coulomb blockade peaks; (iii) an absence of conductance away from particle-hole symmetry at sufficiently low temperatures; and (iv) evidence of a quantum critical point as a function of dot-lead hopping. These properties are compared and contrasted with one dimensional Luttinger systems exhibiting a power-law "tunneling-DOS"., Comment: Real part of the self-energy added to Eq. (2). Accepted for publication in EPJB as a Rapid Note, 4 pages, 3 figures

We investigate the physics of frustrated 3-leg Hubbard ladders in the band limit, when hopping across the ladder's rungs (t$_{\perp}$) is of the same order as hopping along them (t) much greater than the onsite Coulomb repulsion (U). We show that this model exhibits a striking electron-hole asymmetry close to half-filling: the hole-doped system at low temperatures develops a Resonating Valence Bond (RVB)-like d-wave gap (pseudogap close to ($\pi$,0)) coinciding with gapless nodal excitations (nodal liquid); in contrast, the electron-doped system is seen to develop a Mott gap at the nodes, whilst retaining a metallic character of its majority Fermi surface. At lower temperatures in the electron-doped case, d-wave superconducting correlations -- here, coexisting with gapped nodal excitations -- are already seen to arise. Upon further doping the hole-doped case, the RVB-like state yields to d-wave superconductivity. Such physics is reminiscent of that exhibited by the high temperature cuprate superconductors--notably electron-hole asymmetry as noted by Angle Resolved PhotoEmission Spectroscopy (ARPES) and the resistivity exponents observed. This toy model also reinforces the importance of a more thorough experimental investigation of the known 3-leg ladder cuprate systems, and may have some bearing on low dimensional organic superconductors., Comment: 26 pages, 16 figures

We investigate the optical conductivity of half-filled N-leg Hubbard ladders far into the ``deconfinement'' limit (i.e., weak Hubbard interaction and relatively strong interchain hopping). The N-leg Hubbard ladder is equivalent to an N-band model with velocities obeying $v_1=v_N

The electronic structure of the first reported heavy fermion compound without f-electrons LiV_2O_4 was studied by an ab-initio calculation method. In the result of the trigonal splitting and d-d Coulomb interaction one electron of the $d^{1.5}$ configuration of V ion is localized and the rest partially fills a relatively broad conduction band. The effective Anderson impurity model was solved by Non-Crossing-Approximation method, leading to an estimation for the single-site Kondo energy scale T_K. Then, we show how the so-called exhaustion phenomenon of Nozi\`eres for the Kondo lattice leads to a remarkable decrease of the heavy-fermion (or coherence) energy scale $T_{coh}\equiv {T_K}^2/D$ (D is the typical bandwidth), comparable to the experimental result., Comment: 4 pages, RevTeX; 3 figures in format .eps. submitted to PRL

We study the usual one-dimensional Kondo lattice model (1D KLM) using the non-Abelian bosonization formalism. At half-filling, we obtain a Kondo insulator with a gap in both charge and spin excitations which varies quite linearly with the Kondo exchange $J_K$. It consists of a Spin Density Glass state, or a $q=\pi$ spin density wave weakly pinned by a nearly antiferromagnetically ordered spin array. We will analyze the stability of the SDG state in presence of randomness. We will compare these results with those obtained in the one-dimensional Heisenberg-Kondo lattice model (1D HKLM) where the spins are coupled through a large Heisenberg exchange. Away from half-filling, the system is metallic and yields a very small spin gap which is equal to the one-impurity Kondo gap $T_k^{(imp)}$. Unlike the one-impurity Kondo model, we will show why this Kondo phase cannot rule the fixed point of the 1D KLM, away from half-filling. We will rather obtain a normal heavy-fermion state controlled by the energy scale $T_{coh}\sim (T_k^{(imp)})^2/t$ (t is the hopping term) with a quite long-range antiferromagnetic polarization. It is important to notice that both the SDG state and the normal heavy-fermion state are susceptible to occur near a magnetic instability., Comment: 14 pages, 6 figures, (added Latex file)

The Kondo effect in a Tomonaga-Luttinger liquid ($U<

We investigate the one-dimensional Kondo lattice model (1D KLM) for ferromagnetic Kondo couplings. The so-called ferromagnetic 2-leg spin ladder and the S=1 antiferromagnet occur as new one-dimensional Kondo insulators. Both exhibit a spin gap. But, in contrast to the strong coupling limit, the Haldane state which characterizes the 2-leg spin ladder Kondo insulator cannot fight against very weak exterior perturbations. First, by using standard bosonization techniques, we prove that an antiferromagnetic ground state occurs by doping with few holes; it is characterized by a form factor of the spin-spin correlation functions which exhibits two structures respectively at $q=\pi$ and $q=2k_F$. Second, we prove precisely by using renormalization group methods that the Anderson-localization inevitably takes place in that weak-coupling Haldane system, by the introduction of quenched randomness; the spin-fixed point rather corresponds to a ``glass'' state. Finally, a weak-coupling ``analogue'' of the S=1 antiferromagnet Kondo insulator is proposed; we show that the transition into the Anderson-localization state may be avoided in that unusual weak-coupling Haldane system., Comment: 22 pages, TEX and 2 figures (long version); to be published in Phys. Rev. B (December 97)

The one-dimensional Kondo lattice model (1D KLM) is usually defined by the Kondo exchange $J$ between conduction electrons and spins of the array, and the hopping strength t for the moving electrons. Here, we also include a direct exchange $K$ term between spins of the lattice, and we investigate situations where the bare value of $K$ does not exceed $J$. By using the non-Abelian bosonization, we show that a coherent heavy-fermion phase can be stabilized, when the bare value of $K$ exceeds the RKKY exchange (ruled by $T_A\simeq J^2/t$). Conversely, when $K

The major dimensions of ethnicity are examined in this paper. The first section reviews research literature in three content areas--ethnicity, stratification, and communication and in each of these areas generates hypotheses based on the available evidence in sociological, anthropological, and psychological literature. The second section of the paper develops a theoretical model with 31 propositional statements that reflect a concern for the systematic study of ethnicity. (FL)

The questionnaire responses of 768 people from a variety of ethnic groups were analyzed to determine what communication channels were used to link ethnics to their native countries and to provide news of the ethnic community. The relationships between channel preferences and demographics, ethnicity, and communication channel patterns were also examined. The analysis revealed that the four major communication channels used were friends and neighbors (interpersonal communication), radio, local metropolitan daily newspapers, and ethnic-language newspapers. Lower socioeconomic status (SES) respondents relied more on interpersonal communication and on ethnic media, while higher SES respondents turned more to metropolitan media and magazines. Small size of ethnic group was shown to be related to greater importance of interpersonal sources of information--church and correspondence. Suburbanites relied more on metropolitan mass media for news of the ethnic community, while urbanites relied more on friends and neighbors and the church. (FL)