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Monday, 18 July 2011

A Manganite Changes its Stripes

Lawrence Berkeley National Laboratory 
July 15, 2011

If there were a Hall of Fame for materials, manganites would be among its members. Some manganites, compounds of manganese oxides, are renowned for colossal magnetoresistance – the ability to suddenly boost resistance to electrical conductivity by orders of magnitude when a magnetic field is applied – and manganites are also promising candidates for spintronics applications – devices that can manipulate electrons according to their quantum spin as well their charge.

What’s not particularly unusual about manganites, however, is that they have stripes, regions where the material’s electrical charges gather and concentrate. Other so-called correlated-electron materials also have stripes, including many high-temperature superconductors having the same crystal structure: arrangements of layers of atoms named for the mineral perovskite.

Now a team of researchers from the University of Colorado at Boulder, the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), and Argonne National Laboratory have used the technique of angle-resolved photoelectron spectroscopy (ARPES), at beamline 12.0.1 at Berkeley Lab’s Advanced Light Source, to demonstrate a startling new feature of one kind of lanthanum strontium manganese oxide.

This “two-dimensional bilayer manganite” can change its stripes from fluctuating to static and back. As a result, at the right temperature it switches from a metallic state, a good conductor of electricity, to an insulator – a colossal change in conductivity. The researchers report their results in Proceedings of the National Academy of Sciences (PNAS).
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