Superconductivity Research Looks At Higher Temps

Researchers from Stanford University, Menlo Park, Calif., and the Department of Energy's Lawrence Berkeley National Laboratory, Berkeley, Calif., are working to uncover clues to high-temperature (Tc) superconductivity. This data may help resolve a long-standing paradox between different theories of superconductivity and explain how copper-oxide ceramics can superconduct at high temperatures.

To gather this information, researchers used the High Energy Resolution Spectrometer at Berkeley's Advanced Light Source (ALS) facility. Using an angle-resolved photoemission spectroscopy (ARPES), they have been able to study the stripe phase (a new electronic state of solids) and charge- and spin-ordered states in neodymium-substituted lanthanum strontium copper oxide (Nd-LSCO). The technique employs beams of synchrotron light to knock electrons out of the Nd-LSCO sample. The resulting electronic structure then is measured for the energy and the direction of the emitted photoelectrons.

The research team found that at high energies, plots of the sample spectral weights were consistent with charges moving through the Nd-LSCO sample along one-dimensional lines—the so-called stripes. At lower energies, the pattern was more easily explained if the charges were moving in two dimensions. Whether the stripe phase is actually responsible for high-temperature superconductivity remains the subject of debate.