N.C.S.R. "Demokritos"

Research

Department of Materials Science

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Vortex matter properties in high temperature superconductors and MgB2

Our research on superconductivity is focused on the properties of magnetic vortices in high Tc-superconductors cuprates, and MgB2. Flux lines or vortices can be regarded as atoms or molecules of the conventional matter, forming the so called “vortex-matter” where the intervortex distance can easily change by several order of magnitude simply by changing the external magnetic field. In addition, when the mean square displacement of the vortex positions, as the temperature or the magnetic field approaches the Hc2-line is a appreciate fraction of the intervortex spacing the vortex matter can melt. In addition if the anisotropy and small coherence length taken into account vortex matter displays rich phase diagrams, such as ordered vortex solid, Bragg glass solid and liquid phases. Except the academic interest for these issues they are also related with practical applications of the superconductors. The vortex matter phase diagrams and the dynamics of vortices are being investigated by experimental technique based on microscopic Hall sensors SQUID mangetomenty and ac-susceptibility. As research highlights in this area we can include: (a) The single crystal growth and study the vortex matter properties of YBa2Cu33O7-x, HgBa2CuO4, (b) the study of the melting line near Tc and Hc1-line of YBa2Cu33O7-x (c) the role of the geometrical/surface barriers in the magnetic response near Hc1-line of YBa2Cu33O7-x, (d) The preparation and magnetic characterization of pure and aluminum doped MgB2 in polycrystalline form using x-ray diffraction and magnetic measurements, (e) The measurements for the first time of the peak effect in MgB2 single crystals, and (f) the evolution of the magnetic anisotropy and peak effect in carbon and aluminum doped MgB2 single crystals. Our recent research concerns the study of the vortex matter phase diagrams of pure and carbon and aluminum doped MgB2, using high quality single crystals.

Department of Materials Science, N.C.S.R. "Demokritos", 153 10 Aghia Paraskevi, Attiki, phone: +30 210 6503381, fax: +30 210 6519430
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