Three-Dimensional Superconductivity in the Infinite-Layer Compound Sr_{0.9}La_{0.1}CuO_2 in Entire Region below $T_c$

摘要

The infinite-layer compound ACuO$_{2}$ (A $=$ alkaline-earth ions) isregarded as the most suitable material for exploring the fundamental nature ofthe CuO$_2$ plane because it does not contain a charge-reservoir block, such asa rock-salt or a fluorite like block. We report that superconductivity in theinfinite-layer compound Sr$_{0.9}$La$_{0.1}$CuO$_2$ is of a three-dimensionalnature, in contrast to the quasi two-dimensional superconducting behavior ofall other cuprates. The key observation is that the $c$-axis coherence lengthis longer than the $c$-axis lattice constant even at zero temperature. Thismeans that the superconducting order parameter of one CuO$_{2}$ plane overlapswith those of neighboring CuO$_{2}$ planes all the temperatures below the$T_c$. Among all cuprates, only the infinite-layer superconductor shows such afeature.