Charge-Density-Wave Formation in the Doped Two-Leg Extended Hubbard Ladder

We investigate electronic properties of the doped two-leg Hubbard ladder with both the onsite and the nearest-neighbor Coulomb repulsions, by using the the weak-coupling renormalization-group method. It is shown that, for strong nearest-neighbor repulsions, the charge-density-wave state coexisting with the p-density-wave state becomes dominant fluctuation where spins form intrachain singlets. By increasing doping rate, we have also shown that the effects of the nearest-neighbor repulsions are reduced and the system exhibits a quantum phase transition into the d-wave-like (or rung-singlet) superconducting state. We derive the effective fermion theory which describes the critical properties of the transition point with the gapless excitation of magnon. The phase diagram of the two-leg ladder compound, Sr_{14-x}Ca_xCu_{24}O_{41}, is discussed.Comment: 4 pages, 2 figure

Nonmonotonic d_{x^2-y^2} Superconducting Order Parameter in Nd_{2-x}Ce_xCuO_4

Low energy polarized electronic Raman scattering of the electron doped superconductor Nd_1.85Ce_0.15CuO_4 (T_c=22 K) has revealed a nonmonotonic d_{x^2-y^2} superconducting order parameter. It has a maximum gap of 4.4 k_BT_c at Fermi surface intersections with antiferromagnetic Brillouin zone (the ``hot spots'') and a smaller gap of 3.3 k_BT_c at fermionic Brillouin zone boundaries. The gap enhancement in the vicinity of the ``hot spots'' emphasizes role of antiferromagnetic fluctuations and similarity in the origin of superconductivity for electron- and hole-doped cuprates.Comment: 4 pages, 4 figure

Stripe orders in the extended Hubbard model

We study stripe orders of charge and spin density waves in the extended Hubbard model with the nearest-neighbor Coulomb repulsion V within the mean field approximation. We obtain V vs. T(temperature) phase diagram for the on-site Coulomb interaction U/t=8.0 and the filling n=0.8, here t is a nearest-neighbor transfer energy. Our result shows that the diagonal stripe spin density wave state (SDW) is stable for small V, but for large V the most stable state changes to a charge density wave-antiferromagnetic (CDW-AF) state. Especially we find at low temperature and for a certain range of value of V, a vertical stripe CDW-AF state becomes stable.Comment: LaTeX 9 pages, 17 figures, uses jpsj.st

Sensitivity of nucleon-nucleus scattering to the off-shell behavior of on-shell equivalent NN potentials

The sensitivity of nucleon-nucleus elastic scattering to the off-shell behavior of realistic nucleon-nucleon interactions is investigated when on-shell equivalent nucleon-nucleon potentials are used. The study is based on applications of the full-folding optical model potential for an explicit treatment of the off-shell behavior of the nucleon-nucleon effective interaction. Applications were made at beam energies between 40 and 500 MeV for proton scattering from 40Ca and 208Pb. We use the momentum-dependent Paris potential and its local on-shell equivalent as obtained with the Gelfand-Levitan and Marchenko inversion formalism for the two nucleon Schroedinger equation. Full-folding calculations for nucleon-nucleus scattering show small fluctuations in the corresponding observables. This implies that off-shell features of the NN interaction cannot be unambiguously identified with these processes. Inversion potentials were also constructed directly from NN phase-shift data (SM94) in the 0-1.3 GeV energy range. Their use in proton-nucleus scattering above 200 MeV provide a superior description of the observables relative to those obtained from current realistic NN potentials. Limitations and scope of our findings are presented and discussed.Comment: 17 pages tightened REVTeX, 8 .ps figures, submitted to Phys. Rev.

Influence of oxygen ordering kinetics on Raman and optical response in YBa_2Cu_3O_{6.4}

Kinetics of the optical and Raman response in YBa_2Cu_3O_{6.4} were studied during room temperature annealing following heat treatment. The superconducting T_c, dc resistivity, and low-energy optical conductivity recover slowly, implying a long relaxation time for the carrier density. Short relaxation times are observed for the B_{1g} Raman scattering -- magnetic, continuum, and phonon -- and the charge transfer band. Monte Carlo simulations suggest that these two relaxation rates are related to two length scales corresponding to local oxygen ordering (fast) and long chain and twin formation (slow).Comment: REVTeX, 3 pages + 4 PostScript (compressed) figure

Membrane-transferring regions of gp41 as targets for HIV-1 fusion inhibition and viral neutralization

12 páginas, 4 figurasThe fusogenic function of HIV-1 gp41 transmembrane Env subunit relies on two different kinds of structural elements: i) a collapsible ectodomain structure (the hairpin or six-helix bundle) that opens and closes, and ii) two membrane- transferring regions (MTRs), the fusion peptide (FP) and the membrane-proximal external region (MPER), which ensure coupling of hairpin closure to apposition and fusion of cell and viral membranes. The isolation of naturally produced short peptides and neutralizing IgG-s, that interact with FP and MPER, respectively, and block viral infection, suggests that these conserved regions might represent useful targets for clinical intervention. Furthermore, MTR-derived peptides have been shown to be membrane-active. Here, it is discussed the potential use of these molecules and how the analysis of their membrane activity in vitro could contribute to the development of HIV fusion inhibitors and effective immunogensThe authors wish to thank financial support obtained from Spanish MICINN (BIO2008- 00772) (JLN) and University of the Basque Country (GIU 06/42 and DIPE08/12) (NH and JLN).Peer reviewe

Spin correlations in the electron-doped high-transition-temperature superconductor Nd{2-x}Ce{x}CuO{4+/-delta}

High-transition-temperature (high-Tc) superconductivity develops near antiferromagnetic phases, and it is possible that magnetic excitations contribute to the superconducting pairing mechanism. To assess the role of antiferromagnetism, it is essential to understand the doping and temperature dependence of the two-dimensional antiferromagnetic spin correlations. The phase diagram is asymmetric with respect to electron and hole doping, and for the comparatively less-studied electron-doped materials, the antiferromagnetic phase extends much further with doping [1, 2] and appears to overlap with the superconducting phase. The archetypical electron-doped compound Nd{2-x}Ce{x}CuO{4\pm\delta} (NCCO) shows bulk superconductivity above x \approx 0.13 [3, 4], while evidence for antiferromagnetic order has been found up to x \approx 0.17 [2, 5, 6]. Here we report inelastic magnetic neutron-scattering measurements that point to the distinct possibility that genuine long-range antiferromagnetism and superconductivity do not coexist. The data reveal a magnetic quantum critical point where superconductivity first appears, consistent with an exotic quantum phase transition between the two phases [7]. We also demonstrate that the pseudogap phenomenon in the electron-doped materials, which is associated with pronounced charge anomalies [8-11], arises from a build-up of spin correlations, in agreement with recent theoretical proposals [12, 13].Comment: 5 pages, 4 figure

Developing customized stepwise MIRU-VNTR typing for tuberculosis surveillance in Georgia

INTRODUCTION: Mycobacterial Interspersed Repetitive Units-Variable Tandem Repeats (MIRU-VNTR) typing has been widely used for molecular epidemiological studies of tuberculosis (TB). However, genotyping tools for Mycobacterium tuberculosis (Mtb) may be limiting in some settings due to high cost and workload. In this study developed a customized stepwise MIRU-VNTR typing that prioritizes high discriminatory loci and validated this method using penitentiary system cohort in the country of Georgia. METHODS: We used a previously generated MIRU-VNTR dataset from recurrent TB cases (32 cases) in Georgia and a new dataset of TB cases from the penitentiary system (102 cases) recruited from 2014 to 2015. A Hunter-Gaston Discriminatory Index (HGDI) was calculated utilizing a 24 standard loci panel, to select high discriminatory power loci, subsequently defined as the customized Georgia-specific set of loci for initial typing. The remaining loci were scored and hierarchically grouped for second and third step typing of the cohort. We then compared the processing time and costs of the customized stepwise method to the standard 24-loci method. RESULTS: For the customized Georgia-specific set that was used for initial typing, 10 loci were selected with a minimum value of 0.32 to the highest HGDI score locus. Customized 10 loci (step 1) typing of 102 Mtb patient isolates revealed 35.7% clustered cases. This proportion was reduced to 19.5% after hierarchical application of 2nd and 3rd step typing with the corresponding groups of loci. Our customized stepwise MIRU-VNTR genotyping approach reduced the quantity of samples to be typed and therefore overall processing time and costs by 42.6% each. CONCLUSION: Our study shows that our customized stepwise MIRU-VNTR typing approach is a valid alternative of standard MIRI-VNTR typing panels for molecular epidemiological investigation in Georgia that saves time, workload and costs. Similar approaches could be developed for other settings

Resonant Raman Scattering in Antiferromagnets

Two-magnon Raman scattering provides important information about electronic correlations in the insulating parent compounds of high-$T_c$ materials. Recent experiments have shown a strong dependence of the Raman signal in $B_{1g}$ geometry on the frequency of the incoming photon. We present an analytical and numerical study of the Raman intensity in the resonant regime. It has been previously argued by one of us (A.Ch) and D. Frenkel that the most relevant contribution to the Raman vertex at resonance is given by the triple resonance diagram. We derive an expression for the Raman intensity in which we simultaneously include the enhancement due to the triple resonance and a final state interaction. We compute the two-magnon peak height (TMPH) as a function of incident frequency and find two maxima at $\omega^{(1)}_{res} \approx 2\Delta + 3J$ and $\omega^{(2)}_{res} \approx 2\Delta + 8J$. We argue that the high-frequency maximum is cut only by a quasiparticle damping, while the low-frequency maximum has a finite amplitude even in the absence of damping. We also obtain an evolution of the Raman profile from an asymmetric form around $\omega^{(1)}_{res}$ to a symmetric form around $\omega^{(2)}_{res}$. We further show that the TMPH depends on the fermionic quasiparticle damping, the next-nearest neighbor hopping term $t^{\prime}$ and the corrections to the interaction vertex between light and the fermionic current. We discuss our results in the context of recent experiments by Blumberg et al. on $Sr_2CuO_2Cl_2$ and $YBa_2Cu_3O_{6.1}$ and R\"{u}bhausen et al. on $PrBa_2Cu_3O_7$ and show that the triple resonance theory yields a qualitative and to some extent also quantitative understanding of the experimental data.Comment: 19 pages, RevTeX, 16 figures embedded in the text, ps-file is also available at http://lifshitz.physics.wisc.edu/www/morr/morr_homepage.htm