84,148 research outputs found

    Optical properties of Si/Si0.87Ge0.13 multiple quantum well wires

    Get PDF
    Nanometer-scale wires cut into a Si/Si0.87Ge0.13 multiple quantum well structure were fabricated and characterized by using photoluminescence and photoreflectance at temperatures between 4 and 20 K. It was found that, in addition to a low-energy broadband emission at around 0.8 eV and other features normally observable in photoluminescence measurements, fabrication process induced strain relaxation and enhanced electron-hole droplets emission together with a new feature at 1.131 eV at 4 K were observed. The latter was further identified as a transition related to impurities located at the Si/Si0.87Ge0.13 heterointerfaces

    Peak Effect in Superconductors: Melting of Larkin Domains

    Full text link
    Motivated by the recent observations of the peak effect in high-TcT_c YBCO superconductors, we reexamine the origin of this unusual phenomenon. We show that the mechanism based on the kk-dependence (nonlocality) of the vortex-lattice tilt modulus C44(k)C_{44}({\bf k}) cannot account for the essential feature of the peak effect. We propose a scenario in which the peak effect is related to the melting of Larkin domains. In our model, the rise of critical current with increasing temperature is a result of a crossover from the Larkin pinning length to the length scale set by thermally excited free dislocations.Comment: 13 pages, 2 figures, REVTE

    New Models of f(R) Theories of Gravity

    Full text link
    We introduce new models of f(R) theories of gravity that are generalization of Horava-Lifshitz gravity.Comment: 16 pages, typos corrected, v2:minor changes, references adde

    Exchange bias with Fe substitution in LaMnO_3

    Full text link
    The exchange bias (EB) in LaMn_{0.7}Fe_{0.3}O_3 is observed by the negative shift and training effect of the hysteresis loops, while the sample was cooled in external magnetic field. The analysis of cooling field dependence of EB gives the size of the ferromagnetic (FM) cluster ~ 25 Angstrom, where the magnetic anisotropy of FM cluster is found two order of magnitude higher than the FM bulk manganites. We propose that the nanoscale FM clusters are embedded in the glassy magnetic host with EB at the FM/glassy magnetic interface.Comment: 6 figure

    Sub-grid variability in ammonia concentrations and dry deposition in an upland landscape

    Get PDF

    Polarization as a Probe to the Production Mechanisms of Charmonium in πN\pi N Collisions

    Get PDF
    Measurements of the polarization of \jp produced in pion-nucleus collisions are in disagreement with leading twist QCD prediction where \jp is observed to have negligible polarization whereas theory predicts substantial polarization. We argue that this discrepancy cannot be due to poorly known structure functions nor the relative production rates of \jp and χJ\chi_J. The disagreement between theory and experiment suggests important higher twist corrections, as has earlier been surmised from the anomalous non-factorized nuclear AA-dependence of the \jp cross section.Comment: 8 page
    • …
    corecore