33,288 research outputs found

    Improved lattice QCD with quarks: the 2 dimensional case

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    QCD in two dimensions is investigated using the improved fermionic lattice Hamiltonian proposed by Luo, Chen, Xu, and Jiang. We show that the improved theory leads to a significant reduction of the finite lattice spacing errors. The quark condensate and the mass of lightest quark and anti-quark bound state in the strong coupling phase (different from t'Hooft phase) are computed. We find agreement between our results and the analytical ones in the continuum.Comment: LaTeX file (including text + 10 figures

    In-plane ferromagnetism in charge-ordering Na0.55CoO2Na_{0.55}CoO_2

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    The magnetic and transport properties are systematically studied on the single crystal Na0.55CoO2Na_{0.55}CoO_2 with charge ordering and divergency in resistivity below 50 K. A long-range ferromagnetic ordering is observed in susceptibility below 20 K with the magnetic field parallel to Co-O plane, while a negligible behavior is observed with the field perpendicular to the Co-O plane. It definitely gives a direct evidence for the existence of in-plane ferromagnetism below 20 K. The observed magnetoresistance (MR) of 30 % at the field of 6 T at low temperatures indicates an unexpectedly strong spin-charge coupling in triangle lattice systems.Comment: 4 pages, 5 figure

    Comment on "Time-Dependent Density-Matrix Renormalization Group: A Systematic Method for the Study of Quantum Many-Body Out-of- Equilibrium Systems"

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    In a recent Letter [Phys. Rev. Lett. 88, 256403(2002), cond-mat/0109158] Cazalilla and Marston proposed a time-dependent density- matrix renormalization group (TdDMRG) algorithm for the accurate evaluation of out-of-equilibrium properties of quantum many-body systems. For a point contact junction between two Luttinger liquids, a current oscillation develops after initial transient in the insulating regime. Here we would like to point out that (a) the observed oscillation is an artifact of the method; (b) the TdDMRG can be significantly improved by incorporating the non-equilibrium evolution of the goundstate into the density matrix.Comment: 1 page, 2 figure

    Hysteresis and Anisotropic Magnetoresistance in Antiferromagnetic Nd2xCexCuO4Nd_{2-x}Ce_xCuO_{4}

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    The out-of-plane resistivity (ρc\rho_c) and magnetoresistivity (MR) are studied in antiferromangetic (AF) Nd2xCexCuO4Nd_{2-x}Ce_xCuO_{4} single crystals, which have three types of noncollinear antiferromangetic spin structures. The apparent signatures are observed in ρc(T)\rho_c(T) measured at the zero-field and 14 T at the spin structure transitions, giving a definite evidence for the itinerant electrons directly coupled to the localized spins. One of striking feature is an anisotropy of the MR with a fourfold symmetry upon rotating the external field (B) within ab plane in the different phases, while twofold symmetry at spin reorientation transition temperatures. The intriguing thermal hysteresis in ρc(T,B)\rho_c(T,B) and magnetic hysteresis in MR are observed at spin reorientation transition temperatures.Comment: 4 pages, 4 figure

    Oxygen Isotope Effect on the Spin State Transition in (Pr0.7_{0.7}Sm0.3_{0.3})0.7_{0.7}Ca0.3_{0.3}CoO3{_3}

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    Oxygen isotope substitution is performed in the perovskite cobalt oxide (Pr0.7_{0.7}Sm0.3_{0.3})0.7_{0.7}Ca0.3_{0.3}CoO3{_3} which shows a sharp spin state transition from the intermediate spin (IS) state to the low spin (LS) state at a certain temperature. The transition temperature of the spin state up-shifts with the substitution of 16O^{16}O by 18^{18}O from the resistivity and magnetic susceptibility measurements. The up-shift value is 6.8 K and an oxygen isotope exponent (αS\alpha_S) is about -0.8. The large oxygen isotope effect indicates strong electron-phonon coupling in this material. The substitution of 16^{16}O by 18^{18}O leads to a decrease in the frequency of phonon and an increase in the effective mass of electron (mm^\ast), so that the bandwidth W is decreased and the energy difference between the different spin states is increased. This is the reason why the TsT_s is shifted to high temperature with oxygen isotopic exchange.Comment: 4 pages, 3 figure

    Superconductivity and Phase Diagram in (Li0.8_{0.8}Fe0.2_{0.2})OHFeSe1x_{1-x}Sx_x

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    A series of (Li0.8_{0.8}Fe0.2_{0.2})OHFeSe1x_{1-x}Sx_x (0 \leq x \leq 1) samples were successfully synthesized via hydrothermal reaction method and the phase diagram is established. Magnetic susceptibility suggests that an antiferromagnetism arising from (Li0.8_{0.8}Fe0.2_{0.2})OH layers coexists with superconductivity, and the antiferromagnetic transition temperature nearly remains constant for various S doping levels. In addition, the lattice parameters of the both a and c axes decrease and the superconducting transition temperature Tc_c is gradually suppressed with the substitution of S for Se, and eventually superconductivity vanishes at xx = 0.90. The decrease of Tc_c could be attributed to the effect of chemical pressure induced by the smaller ionic size of S relative to that of Se, being consistent with the effect of hydrostatic pressure on (Li0.8_{0.8}Fe0.2_{0.2})OHFeSe. But the detailed investigation on the relationships between TcT_{\rm c} and the crystallographic facts suggests a very different dependence of TcT_{\rm c} on anion height from the Fe2 layer or ChCh-Fe2-ChCh angle from those in FeAs-based superconductors.Comment: 6 pages, 6 figure

    Bound States and Critical Behavior of the Yukawa Potential

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    We investigate the bound states of the Yukawa potential V(r)=λexp(αr)/rV(r)=-\lambda \exp(-\alpha r)/ r, using different algorithms: solving the Schr\"odinger equation numerically and our Monte Carlo Hamiltonian approach. There is a critical α=αC\alpha=\alpha_C, above which no bound state exists. We study the relation between αC\alpha_C and λ\lambda for various angular momentum quantum number ll, and find in atomic units, αC(l)=λ[A1exp(l/B1)+A2exp(l/B2)]\alpha_{C}(l)= \lambda [A_{1} \exp(-l/ B_{1})+ A_{2} \exp(-l/ B_{2})], with A1=1.020(18)A_1=1.020(18), B1=0.443(14)B_1=0.443(14), A2=0.170(17)A_2=0.170(17), and B2=2.490(180)B_2=2.490(180).Comment: 15 pages, 12 figures, 5 tables. Version to appear in Sciences in China

    Novel dynamical effects and glassy response in strongly correlated electronic system

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    We find an unconventional nucleation of low temperature paramagnetic metal (PMM) phase with monoclinic structure from the matrix of high-temperature antiferromagnetic insulator (AFI) phase with tetragonal structure in strongly correlated electronic system BaCo0.9Ni0.1S1.97BaCo_{0.9}Ni_{0.1}S_{1.97}. Such unconventional nucleation leads to a decease in resistivity by several orders with relaxation at a fixed temperature without external perturbation. The novel dynamical process could arise from the competition of strain fields, Coulomb interactions, magnetic correlations and disorders. Such competition may frustrate the nucleation, giving rise to a slow, nonexponential relaxation and "physical aging" behavior.Comment: 5 pages, 4 figure

    Intelligent Modeling and Verification (Editorial)

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