Gonnelli R S, Daghero D, Tortello M, Ummarino G A, Bukowski Z, Karpinski J, Reuvekamp P G, Kremer R K, Profeta G, Suzuki K, Kuroki K
Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino, Italy.
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław, Poland.
Sci Rep. 2016 May 24;6:26394. doi: 10.1038/srep26394.
Iron-based compounds (IBS) display a surprising variety of superconducting properties that seems to arise from the strong sensitivity of these systems to tiny details of the lattice structure. In this respect, systems that become superconducting under pressure, like CaFe2As2, are of particular interest. Here we report on the first directional point-contact Andreev-reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure, and on the interpretation of the results using a 3D model for Andreev reflection combined with ab-initio calculations of the Fermi surface (within the density functional theory) and of the order parameter symmetry (within a random-phase-approximation approach in a ten-orbital model). The almost perfect agreement between PCARS results at different pressures and theoretical predictions highlights the intimate connection between the changes in the lattice structure, a topological transition in the holelike Fermi surface sheet, and the emergence on the same sheet of an order parameter with a horizontal node line.
铁基化合物（IBS）展现出令人惊讶的多种超导特性，这些特性似乎源于这些体系对晶格结构微小细节的强烈敏感性。在这方面，像CaFe2As2这样在压力下成为超导体的体系特别令人感兴趣。在此，我们报告了在准静水压下对CaFe2As2晶体进行的首次定向点接触安德烈夫反射光谱（PCARS）测量，以及使用安德烈夫反射的三维模型结合费米面的从头计算（在密度泛函理论范围内）和序参量对称性的从头计算（在十轨道模型的随机相位近似方法范围内）对结果的解释。不同压力下PCARS结果与理论预测之间几乎完美的一致性突出了晶格结构变化、空穴型费米面片上的拓扑转变以及同一费米面片上具有水平节点线的序参量出现之间的紧密联系。
