Li L, Zheng Q, Zou Q, Rajput S, Ijaduola A O, Wu Z, Wang X P, Cao H B, Somnath S, Jesse S, Chi M, Gai Z, Parker D, Sefat A S
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Sci Rep. 2017 Apr 19;7(1):949. doi: 10.1038/s41598-017-00984-1.
Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFeAs-based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Néel-ordering temperature in BaFeAs crystal (T = 132 K to 136 K) by improving in-plane electronic defects and reducing overall a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFeAs crystal (T = 23 to 25 K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. While annealing improves local chemical and electronic uniformity resulting in higher T in the parent, it promotes nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystal regions, which lead to both higher overall T and critical-current-density, J .
诸如反铁磁体或超导体之类的量子材料很复杂，因为原子尺度上的化学、电子和自旋现象会在其集体特性中表现出来。尽管在设计此类材料方面有一些线索，但它们在很大程度上仍然不可预测。在这项工作中，我们发现通过热退火消除局部晶格应变和电子结构无序会导致基于BaFeAs的晶体的转变温度升高。退火通过改善面内电子缺陷并减小整体a晶格参数来提高BaFeAs晶体中的奈尔有序温度（T = 132 K至136 K），同时通过析出钴掺杂剂并给出更大的整体a晶格参数来提高最佳钴掺杂的BaFeAs晶体中的超导有序温度（T = 23至25 K）。退火改善了母体中的局部化学和电子均匀性，从而导致更高的T，同时它促进了超导体中的纳米级相分离，导致主导晶体区域中的差异更小和超导带隙更强，这导致了更高的整体T和临界电流密度Jc。
