Takahashi Hiroki, Igawa Kazumi, Arii Kazunobu, Kamihara Yoichi, Hirano Masahiro, Hosono Hideo
Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan.
Nature. 2008 May 15;453(7193):376-8. doi: 10.1038/nature06972. Epub 2008 Apr 23.
The iron- and nickel-based layered compounds LaOFeP (refs 1, 2) and LaONiP (ref. 3) have recently been reported to exhibit low-temperature superconducting phases with transition temperatures T(c) of 3 and 5 K, respectively. Furthermore, a large increase in the midpoint T(c) of up to approximately 26 K has been realized in the isocrystalline compound LaOFeAs on doping of fluoride ions at the O2- sites (LaO(1-x)F(x)FeAs). Experimental observations and theoretical studies suggest that these transitions are related to a magnetic instability, as is the case for most superconductors based on transition metals. In the copper-based high-temperature superconductors, as well as in LaOFeAs, an increase in T(c) is often observed as a result of carrier doping in the two-dimensional electronic structure through ion substitution in the surrounding insulating layers, suggesting that the application of external pressure should further increase T(c) by enhancing charge transfer between the insulating and conducting layers. The effects of pressure on these iron oxypnictide superconductors may be more prominent than those in the copper-based systems, because the As ion has a greater electronic polarizability, owing to the covalency of the Fe-As chemical bond, and, thus, is more compressible than the divalent O2- ion. Here we report that increasing the pressure causes a steep increase in the onset T(c) of F-doped LaOFeAs, to a maximum of approximately 43 K at approximately 4 GPa. With the exception of the copper-based high-T(c) superconductors, this is the highest T(c) reported to date. The present result, together with the great freedom available in selecting the constituents of isocrystalline materials with the general formula LnOTMPn (Ln, Y or rare-earth metal; TM, transition metal; Pn, group-V, 'pnicogen', element), indicates that the layered iron oxypnictides are promising as a new material platform for further exploration of high-temperature superconductivity.
最近有报道称，铁基和镍基层状化合物LaOFeP（参考文献1、2）和LaONiP（参考文献3）分别呈现出转变温度T(c)为3 K和5 K的低温超导相。此外，在O2-位点掺杂氟离子的等晶化合物LaOFeAs（LaO(1-x)F(x)FeAs）中，中点T(c)大幅提高，最高可达约26 K。实验观察和理论研究表明，这些转变与磁不稳定性有关，大多数基于过渡金属的超导体都是如此。在铜基高温超导体以及LaOFeAs中，通过在周围绝缘层中进行离子取代，二维电子结构中的载流子掺杂通常会导致T(c)升高，这表明施加外部压力应通过增强绝缘层和导电层之间的电荷转移来进一步提高T(c)。压力对这些铁基氧族元素超导体的影响可能比铜基体系更为显著，因为由于Fe-As化学键的共价性，As离子具有更大的电子极化率，因此比二价O2-离子更易压缩。在此我们报道，增加压力会使F掺杂的LaOFeAs的起始T(c)急剧升高，在约4 GPa时最高可达约43 K。除铜基高温超导体外，这是迄今为止报道的最高T(c)。目前的结果，以及在选择通式为LnOTMPn（Ln为Y或稀土金属；TM为过渡金属；Pn为第V族“氮族”元素）的等晶材料成分时所具有的极大自由度，表明层状铁基氧族元素有望成为进一步探索高温超导性的新型材料平台。
