US researchers studying high-temperature cuprate superconductors outside the superconducting regime have used cutting-edge X-ray scattering to detect long-predicted – but never previously observed – excitations called plasmons perpendicular to the material’s atomic planes. Researchers hope the findings may help theorists to understand these highly unusual materials better, and perhaps even guide the quest for room-temperature superconductors.
The cuprate superconductors are archetypal “strongly correlated” materials, which are difficult to describe using current approximate models. “In most theories we have today you try to catch the main interaction and treat the others as a small perturbation,” explains condensed matter physicist Wei-Sheng Lee of Stanford University in California, “But for these strongly correlated materials, all the interactions are equally important.”
The materials therefore baffle theoreticians. For example, whereas the established BCS theory of superconductivity predicts that the property should disappear above about 30 K, some cuprates remain superconducting at temperatures up to 130 K. Something seems to preserve the superconducting state at relatively high temperatures, but what it is remains unclear.
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