Volume 2 Issue 3, March 2006
Superconductivity arises when electrons form pairs that condense into a coherent ground–state. The symmetry of the pairing determines the overall superconducting behaviour, including the transition temperature, T c. In high–T c superconductors, the pairing has d–wave symmetry, which changes sign four times on rotation through 360°. Using their celebrated phase-sensitive technique, John Kirtley and co–authors revisit optimally doped YBa2Cu3O7–8 to map out the in–plane angular dependence of the pairing symmetry. A square pick–up loop scans over the arrangement of 72 rings to detect any spontaneous supercurrents (shown as peaks in the image). Owing to the presence of Cu–O chains along one crystalline axis, the superconducting energy gap is larger in that direction. The authors also find no evidence for time-reversal symmetry breaking and set an upper bound to any imaginary components of the main d–wave gap. [Article p190]
Editorial
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