Magnetic-field effects on the in-plane electrical resistivity in the single-crystal La2−x_{2-x}Bax_xCuO4_4 and La1.6−x_{1.6-x}Nd0.4_{0.4}Srx_xCuO4_4 around x=1/8x=1/8: Relating to the field-induced stripe order

Temperature dependence of the in-plane electrical resistivity, $\rho_{\rm ab}$, in various magnetic fields has been measured in the single-crystal La$_{2-x}$Ba$_x$CuO$_4$ with $x=0.08$, 0.10, 0.11 and La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ with $x=0.12$. It has been found that the superconducting transition curve shows a so-called fan-shape broadening in magnetic fields for $x=0.08$, while it shifts toward the low-temperature side in parallel with increasing field for $x=0.11$ and 0.12 where the charge-spin stripe order is formed at low temperatures. As for $x=0.10$, the broadening is observed in low fields and it changes to the parallel shift in high fields above 9 T. Moreover, the normal-state value of $\rho_{\rm ab}$ at low temperatures markedly increases with increasing field up to 15 T. It is possible that these pronounced features of $x=0.10$ are understood in terms of the magnetic-field-induced stabilization of the stripe order suggested from the neutron-scattering measurements in the La-214 system. The $\rho_{\rm ab}$ in the normal state at low temperatures has been found to be proportional to ln(1/$T$) for $x=0.10$, 0.11 and 0.12. The ln(1/$T$) dependence of $\rho_{\rm ab}$ is robust even in the stripe-ordered state.Comment: 6 pages, 4 figures, ver. 2 has been accepted for publication in Phys. Rev.

Out-of-plane dielectric constant and insulator-superconductor transition in Bi_2Sr_2Dy_{1-x}Er_xCu_2O_8 single crystals

The out-of-plane dielectric constant of the parent insulator of the high-temperature superconductor Bi_2Sr_2(Dy,Er)Cu_2O_8 was measured and analysed from 80 to 300 K in the frequency range of 10^6-10^9 Hz. All the samples were found to show a fairly large value of 10-60, implying some kind of charge inhomogeneity in the CuO_2 plane. Considering that the superconducting sample Bi_2Sr_2(Ca,Pr)Cu_2O_8 also shows a similar dielectric constant, the charge inhomogeneity plays an important role in the insulator-superconductor transition.Comment: RevTex4 format, 5 pages, 3 figures, submitted to J. Phys. Condens. Ma

QUANTUM ERROR-CORRECTION FOR SPATIALLY CORRELATED ERRORS

It is shown that errors due to spatially correlated noises can be corrected by the quantumerror-correction code and error-correction procedure prepared for those for independentnoises. A model of noisy-channel which is under the influence of spatially correlated quantumBrownian motion is investigated within the framework of non-equilibrium thermofield dynamics that is a canonical operator formalism for dissipative quantum systems

Levantamento preliminar de viroses de plantas cultivadas nos arredores de Manaus, Am

Um levantamento preliminar de viroses de plantas cultivadas nos arredores de Manaus foi feito em março de 1977. Diversas propriedades particulares e campos experimentais foram inspecionados, anotando-se as plantas exibindo sintomatologia suspeita. A verificação da sua possível etiologia viral foi feita através de testes de transmissão, serologia e exames electrono microscópicos. Foram constatadas diversas viroses em tomateiro, pimentão, quiabeiro, feijoeiro, cucurbitáceas, soja, feijão-de-asa, milho. etc. Como regra geral, ao contrário do que sucede no Sul do País, as viroses transmitidas por afídeos foram de ocorrência rara, presumivelmente porque as condições climáticas da região seriam desfavoráveis à biologia desses insetos

Vibrationally resolved partial cross sections and asymmetry parameters for carbon K-shell photoionization of the CO_2 molecule

We have measured the vibrationally resolved partial cross sections \sigma_{v_1^{\prime}} and asymmetry parameters \beta_{v_1^{\prime}} for C K-shell photoionization of the CO2 molecule in the Σu shape resonance region above the C K-shell ionization threshold. The positions of both the maxima of \sigma_{v_1^{\prime}} and the minima of \beta_{v_1^{\prime}} move towards the C K-shell threshold with increasing symmetric stretching vibrational excitation v'1 in the C 1s single-hole state. Calculations employing the relaxed-core Hartree–Fock approach reproduce the observed vibrational effects

Ultrafast dynamics of coherent optical phonons and nonequilibrium electrons in transition metals

The femtosecond optical pump-probe technique was used to study dynamics of photoexcited electrons and coherent optical phonons in transition metals Zn and Cd as a function of temperature and excitation level. The optical response in time domain is well fitted by linear combination of a damped harmonic oscillation because of excitation of coherent $E_{2g}$ phonon and a subpicosecond transient response due to electron-phonon thermalization. The electron-phonon thermalization time monotonically increases with temperature, consistent with the thermomodulation scenario, where at high temperatures the system can be well explained by the two-temperature model, while below $\approx$ 50 K the nonthermal electron model needs to be applied. As the lattice temperature increases, the damping of the coherent $E_{2g}$ phonon increases, while the amplitudes of both fast electronic response and the coherent $E_{2g}$ phonon decrease. The temperature dependence of the damping of the $E_{2g}$ phonon indicates that population decay of the coherent optical phonon due to anharmonic phonon-phonon coupling dominates the decay process. We present a model that accounts for the observed temperature dependence of the amplitude assuming the photoinduced absorption mechanism, where the signal amplitude is proportional to the photoinduced change in the quasiparticle density. The result that the amplitude of the $E_{2g}$ phonon follows the temperature dependence of the amplitude of the fast electronic transient indicates that under the resonant condition both electronic and phononic responses are proportional to the change in the dielectric function.Comment: 10 pages, 9 figures, to appear in Physical Review

Low-energy electron scattering by CH_3F, CH_2F_2, CHF_3, and CF_4

We present measured and calculated differential cross sections, as well as calculated integral cross sections, for elastic electron collisions with CH_3F, CH_2F_2, CHF_3, and CF_4. The calculated cross sections were obtained with the Schwinger multichannel method, and a Born-closure procedure was used to improve the differential cross sections for polar systems. Polarization effects were found to be relevant even for systems with moderately large permanent dipole moments, such as CH_3F and CHF_3. In general, there is good agreement between theory and experiment