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Electrons in Single File Provide New Insights

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  • RemyC
    From: http://www.physorg.com/news2067.html Superconductivity Breakthrough - Electrons in Single File Provide New Insights November 22, 2004 A team at the
    Message 1 of 1 , Nov 26 5:49 AM
      From:
      http://www.physorg.com/news2067.html

      Superconductivity Breakthrough - Electrons in Single File Provide New
      Insights

      November 22, 2004

      A team at the University of Innsbruck has been successful in conducting
      electrons in metals along predetermined channels. This behaviour, observed
      for the first time in metals, provides important insights into the
      interactions of electrons - and on how the phenomenon of the current flow
      without any resistance loss, termed superconductivity, can occur. Thereby
      this project aided by the Austrian Science Fund (FWF) combines fundamental
      research, at its best, with potential applications in the future.

      Image of a platinum surface with structured chains of individual atoms, made
      visible by scanning tunnelling electron microscopy. (© Erminald Bertel)

      High-temperature superconductors are ceramic materials that conduct
      electricity without resistance, and thus without loss, below a certain
      temperature. At higher temperatures, the behaviour rapidly changes and
      experiences resistance. Such discontinuous changes due to external
      influences are typical for the so-called "smart materials". Their
      discontinuous behaviour is closely linked with a mutual dependence of
      spatially confined electrons, giving rise to a commonly coordinated motion
      pattern. So far this dependence termed as correlation had been observed only
      in non-metals.

      Electrons in Single File...

      Now a team under Prof. Erminald Bertel, Institute of Physical Chemistry,
      University of Innsbruck, has for the first time succeeded in forcing the
      electrons in a metal as well into such a mutual dependence. For this
      purpose, the researchers first of all created nano-structures on the surface
      of metal single crystals, which are crystals with uniform lattice structure.

      Prof. Bertel, the project director, explains: "Normally, the electrons in a
      metal spread in all three directions in space. But in metal single crystals,
      some of the electrons are confined to the surface and therefore can move
      only in two dimensions. Nano-structures can then further restrict their
      freedom of movement. To produce such structures, the surfaces of copper
      crystals for instance can be oxidised in such a way that free copper
      channels of 3 nanometres width lie between ridges of copper oxide. In these
      channels, the electrons can only move unidimensionally. Also on platinum
      crystals atom chains can be arranged to run parallel across the surface with
      approximately 0.8 nanometre spacing. Certain electrons can then only spread
      along these chains."

      Once the electrons were forced into a controlled motion along the channels
      or chains, Professor Bertel's team was able to observe something
      fascinating - depending on experimental conditions, the electrons move
      within the individual channels entirely independent of each other, i.e.
      incoherently, or they align their movements across all channels. In such a
      state of motion that is described as coherent, the electrons can no longer
      be assigned to individual channels, but are "de-localised".

      .When the Temperature is Right

      For a closer analysis of the states of the electrons, the researchers at
      Innsbruck also made use of photoelectron spectroscopy. In this method, the
      energetic distribution of electrons emitted from the surface due to light
      (photon) absorption is measured. Interestingly, the spectra showed that
      above a critical temperature, the electrons pass from a coherent into an
      incoherent state.

      A completely similar temperature dependence of photoelectron spectra,
      however, is already known in superconductors, but was explained differently
      so far. Thus the observations of the Innsbruck team suggest that the
      superconductivity in ceramic superconductors is connected to a transition of
      electrons from an incoherent state into a coherent state.

      Prof. Bertel: "The transport of electricity without loss due to electric
      resistance could mean a significant contribution to energy saving and to the
      solution of some environmental problems. But at present our comprehension of
      superconductivity does not allow the synthesis of superconductive materials
      that can afford a commercial use under economical conditions. Our team has
      achieved in adding a small chip to the mosaic, which brings us a little
      closer to such applications."

      Source: Public Relations für Research and Development
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