59,271 research outputs found

    Emergent nanoscale superparamagnetism at oxide interfaces

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    Atomically sharp oxide heterostructures exhibit a range of novel physical phenomena that do not occur in the parent bulk compounds. The most prominent example is the appearance of highly conducting and superconducting states at the interface between the band insulators LaAlO3 and SrTiO3. Here we report a new emergent phenomenon at the LaMnO3/SrTiO3 interface in which an antiferromagnetic insulator abruptly transforms into a magnetic state that exhibits unexpected nanoscale superparamagnetic dynamics. Upon increasing the thickness of LaMnO3 above five unit cells, our scanning nanoSQUID-on-tip microscopy shows spontaneous formation of isolated magnetic islands of 10 to 50 nm diameter, which display random moment reversals by thermal activation or in response to an in-plane magnetic field. Our charge reconstruction model of the polar LaMnO3/SrTiO3 heterostructure describes the sharp emergence of thermodynamic phase separation leading to nucleation of metallic ferromagnetic islands in an insulating antiferromagnetic matrix. The model further suggests that the nearby superparamagnetic-ferromagnetic transition can be gate tuned, holding potential for applications in magnetic storage and spintronics

    Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin films

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    We present a detailed study on the magnetic properties, including anisotropy, reversal fields, and magnetization reversal processes, of well characterized half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3 (STO) substrates with three different surface orientations, i.e. (001), (110) and (1-18). The latter shows step edges oriented parallel to the [110] (in-plane) crystallographic direction. Room temperature high resolution vectorial Kerr magnetometry measurements have been performed at different applied magnetic field directions in the whole angular range. In general, the magnetic properties of the LSMO films can be interpreted with just the uniaxial term with the anisotropy axis given by the film morphology, whereas the strength of this anisotropy depends on both structure and film thickness. In particular, LSMO films grown on nominally flat (110)-oriented STO substrates presents a well defined uniaxial anisotropy originated from the existence of elongated in-plane [001]-oriented structures, whereas LSMO films grown on nominally flat (001)-oriented STO substrates show a weak uniaxial magnetic anisotropy with the easy axis direction aligned parallel to residual substrate step edges. Elongated structures are also found for LSMO films grown on vicinal STO(001) substrates. These films present a well-defined uniaxial magnetic anisotropy with the easy axis lying along the step edges and its strength increases with the LSMO thickness. It is remarkable that this step-induced uniaxial anisotropy has been found for LSMO films up to 120 nm thickness. Our results are promising for engineering novel half-metallic magnetic devices that exploit tailored magnetic anisotropy.Comment: 10 pages, 10 figures, 1 tabl

    Mapping Big Data into Knowledge Space with Cognitive Cyber-Infrastructure

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    Big data research has attracted great attention in science, technology, industry and society. It is developing with the evolving scientific paradigm, the fourth industrial revolution, and the transformational innovation of technologies. However, its nature and fundamental challenge have not been recognized, and its own methodology has not been formed. This paper explores and answers the following questions: What is big data? What are the basic methods for representing, managing and analyzing big data? What is the relationship between big data and knowledge? Can we find a mapping from big data into knowledge space? What kind of infrastructure is required to support not only big data management and analysis but also knowledge discovery, sharing and management? What is the relationship between big data and science paradigm? What is the nature and fundamental challenge of big data computing? A multi-dimensional perspective is presented toward a methodology of big data computing.Comment: 59 page

    R.F. planar magnetron sputtered ZnO films I: structural properties

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    The structural properties of r.f. planar magnetron sputtered ZnO films are studied as a function of deposition parameters: substrate type, substrate temperature, sputter gas pressure, growth rate and sputtering power.\ud \ud These films are applied as piezoelectric transducers in micromechanical sensors and actuators. The electric properties, and consequently the piezoelectric behaviour, depend strongly on the structural properties of the layers.\ud \ud All films are polycrystalline. The individual grains are highly oriented with their crystallographic c axis perpendicular to the substrate. Crystalline substrates such as silicon or SiO2 induce a growth of small grains, a few hundredths of a micron wide and long. Amorphous substrates such as metals or amorphous SiO2 induce a growth of broad columnar grains extending through the film thickness and a few tenths of a micron wide. Trends in density and grain size are in agreement with Thornton's structure zone model

    Tailored nano-antennas for directional Raman studies of individual carbon nanotubes

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    We exploit the near field enhancement of nano-antennas to investigate the Raman spectra of otherwise not optically detectable carbon nanotubes (CNTs). We demonstrate that a top-down fabrication approach is particularly promising when applied to CNTs, owing to the sharp dependence of the scattered intensity on the angle between incident light polarization and CNT axis. In contrast to tip enhancement techniques, our method enables us to control the light polarization in the sample plane, locally amplifying and rotating the incident field and hence optimizing the Raman signal. Such promising features are confirmed by numerical simulations presented here. The relative ease of fabrication and alignment makes this technique suitable for the realization of integrated devices that combine scanning probe, optical, and transport characterization

    Ultracold Atoms as a Target: Absolute Scattering Cross-Section Measurements

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    We report on a new experimental platform for the measurement of absolute scattering cross-sections. The target atoms are trapped in an optical dipole trap and are exposed to an incident particle beam. The exponential decay of the atom number directly yields the absolute total scattering cross-section. The technique can be applied to any atomic or molecular species that can be prepared in an optical dipole trap and provides a large variety of possible scattering scenarios

    Laser writing of individual atomic defects in a crystal with near-unity yield

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    Atomic defects in wide band gap materials show great promise for development of a new generation of quantum information technologies, but have been hampered by the inability to produce and engineer the defects in a controlled way. The nitrogen-vacancy (NV) color center in diamond is one of the foremost candidates, with single defects allowing optical addressing of electron spin and nuclear spin degrees of freedom with potential for applications in advanced sensing and computing. Here we demonstrate a method for the deterministic writing of individual NV centers at selected locations with high positioning accuracy using laser processing with online fluorescence feedback. This method provides a new tool for the fabrication of engineered materials and devices for quantum technologies and offers insight into the diffusion dynamics of point defects in solids.Comment: 16 pages, 8 figure

    Search for New Physics in SHiP and at future colliders

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    SHiP is a newly proposed fixed-target experiment at the CERN SPS with the aim of searching for hidden particles that interact very weakly with SM particles. The work presented in this document investigates SHiP's physics reach in the parameter space of the Neutrino Minimal Standard Model (ν\nuMSM), which is a theory that could solve most problems left open by the Standard Model with sterile neutrinos. A model introducing an extra U(1)U(1) symmetry in the hidden sector, providing a natural candidate for dark matter, is also explored. This work shows that the SHiP experiment can improve by several orders of magnitude the sensitivity to Heavy Neutral Leptons below 2 GeV, scanning a large part of the parameter space below the BB meson mass. The remainder of the ν\nuMSM parameter space, dominated by right-handed neutrinos with masses above 2 GeV, can be explored at a future e+ee^+e^- collider. Similarly, SHiP can greatly improve present constraints on U(1)U(1) dark photons.Comment: Proceedings for the INFIERI 2014 schoo
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