1,502 research outputs found

    Spin-charge separation in Aharonov-Bohm rings of interacting electrons

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    We investigate the properties of strongly correlated electronic models on a flux-threaded ring connected to semi-infinite free-electron leads. The interference pattern of such an Aharonov-Bohm ring shows sharp dips at certain flux values, determined by the filling, which are a consequence of spin-charge separation in a nanoscopic system.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let

    Superconductivity with s and p-symmetries in an extended Hubbard model with correlated hopping

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    We consider a generalized Hubbard model with on-site and nearest-neighbour repulsions U and V respectively, and nearest-neighbour hopping for spin up (down) which depends on the total occupation n_b of spin down (up) electrons on both sites involved. The hopping parameters are t_{AA}, t_{AB} and t_{BB} for n_b=0,1,2 respectively. We briefly summarize results which support that the model exhibits s-wave superconductivity for certain parameters and extend them by studying the Berry phases. Using a generalized Hartree-Fock(HF) BCS decoupling of the two and three-body terms, we obtain that at half filling, for t_{AB}<t_{AA}=t_{BB} and sufficiently small U and V the model leads to triplet p-wave superconductivity for a simple cubic lattice in any dimension. In one dimension, the resulting phase diagram is compared with that obtained numerically using two quantized Berry phases (topological numbers) as order parameters. While this novel method supports the previous results, there are quantitative differences.Comment: Latex file, 14 pages, 2 postscript figure

    Critical behavior of the S=3/2 antiferromagnetic Heisenberg chain

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    Using the density-matrix renormalization-group technique we study the long-wavelength properties of the spin S=3/2 nearest-neighbor Heisenberg chain. We obtain an accurate value for the spin velocity v=3.8+- 0.02, in agreement with experiment. Our results show conclusively that the model belongs to the same universality class as the S=1/2 Heisenberg chain, with a conformal central charge c=1 and critical exponent eta=1Comment: RevTeX (version 3.0), 4 twocolumn pages with 4 embedded figure

    Evidence of quantum criticality in the doped Haldane system Y2BaNiO5

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    Experimental bulk susceptibility X(T) and magnetization M(H,T) of the S=1-Haldane chain system doped with nonmagnetic impurities, Y2BaNi1-xZnxO5 (x=0.04,0.06,0.08), are analyzed. A numerical calculation for the low-energy spectrum of non-interacting open segments describes very well experimental data above 4 K. Below 4 K, we observe power-law behaviors, X(T)=T^-alpha and M(H,T)/T^(1-alpha)=f(alpha,(H/T)), with alpha (<1) depending on the doping concentration x.This observation suggests the appearance of a gapless quantum phase due to a broad distribution of effective couplings between the dilution-induced moments.Comment: 4 pages, 3 figure

    Features of spin-charge separation in the equilibrium conductance through finite rings

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    We calculate the conductance through rings with few sites LL described by the t−Jt-J model, threaded by a magnetic flux Φ\Phi and weakly coupled to conducting leads at two arbitrary sites. The model can describe a circular array of quantum dots with large charging energy UU in comparison with the nearest-neighbor hopping tt. We determine analytically the particular values of Φ\Phi for which a depression of the transmittance is expected as a consequence of spin-charge separation. We show numerically that the equilibrium conductance at zero temperature is depressed at those particular values of Φ\Phi for most systems, in particular at half filling, which might be easier to realize experimentally.Comment: 8 pages, 7 figure

    Spin-charge separation in strongly interacting finite ladder rings

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    We study the conductance through Aharonov-Bohm finite ladder rings with strongly interacting electrons, modelled by the prototypical t-J model. For a wide range of parameters we observe characteristic dips in the conductance as a function of magnetic flux, predicted so far only in chains which are a signature of spin and charge separation. These results open the possibility of observing this peculiar many-body phenomenon in anisotropic ladder systems and in real nanoscopic devices.Comment: 4 pages, 6 figure
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