Mar 9, 2007
Superconductivity and magnetism in harmony in a novel nanomaterial
Magnetism and superconductivity are often thought to be incompatible. However, physicists in the US and France have created a nanoscale structure that contains both magnetic and superconducting properties at the same time. The results show a hitherto undocumented interplay between ferromagnetism and superconductivity and the researchers will be studying the phenomenon at the Swiss Light Source, at the Paul Scherrer Institute, over the next two years.
According to the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons with opposite spins form pairs that can move through a material without resistance. A magnetic field can destroy superconductivity in two ways: by breaking up the electron pair, or by trying to make both of the electron spins point in the same direction. These effects also limit how much current can flow through the superconductor because of the disruptive effect of the magnetic field produced by the current itself.
Last year, Jacques Chakhalian and colleagues at the Max Planck Institute, Germany, and the University of Grenoble, France, published a paper in Nature Physics, documenting novel properties at the interface between a superconductor made from yttrium, barium copper and oxygen and a ferromagnet made from lanthanum calcium manganese oxide (LCMO). The researchers developed a technique that allowed them to combine the two materials in one thin-film superlattice, which showed both superconducting and magnetic properties.
Chakhalian and colleagues now plan to look more closely at the interface between the two materials using synchrotron light (electromagnetic radiation of varying wavelengths that can be tuned to a specific wavelength for a particular experiment). To help them do this, the researchers have been awarded research time and financial support over the next two years, at the Swiss Light Source – the most advanced synchrotron light source in the world.
The spectrum at the Swiss Light Source varies from infrared light to soft and hard X-rays. However, unlike conventional X-rays, which diffuse through space, the light beams from the synchrotron are sharply focused. The main technical challenge for Chakhalian and his team will now be to focus the beam of low-energy photons into a spot the size of a few hundred microns.
The work will open up a new area of physics and could even lead to the discovery of more materials with both magnetic and superconducting properties, say the researchers.