铁基超导体

铁基超导体是指化合物中含有铁，在低温时具有超导现象，且铁扮演形成超导的主体的材料。2006年日本东京工业大学细野秀雄教授的团队发现第一个以铁为超导主体的化合物LaFeOP^[1]，打破以往普遍认定铁元素不利形成超导迷思。

LnFePnO的晶体结构，它是ferropnictide化合物之一。

根据BCS理论，产生超导性的必要条件是材料中的电子必须配对，这样配对的电子称为库柏对。库柏对中的两个电子自旋相反，所以总自旋为零，因而科学家认为超导性与铁磁性可能无法共存，材料中如果加入磁性元素（如铁、镍）会大大降低超导性。铁基超导体虽然含有铁元素且是产生超导的主体，但是铁和其他元素（如砷、硒）形成铁基平面后，已不再具有铁磁性。

2008年1月9日，细野秀雄教授的团队再度发现铁基层状材料La[O_1-xF_x]FeAs（x = 0.05 – 0.12）在绝对温度26K时存在超导性^[2]。2008年2月26日，细野团队又发现其在绝对温度43 K的超导性^[3]。2008年3月28日，中国科学院物理研究所赵忠贤领导的科研小组报告，氟掺杂镨氧铁砷化合物的高温超导临界温度可达52 K（-221.15 ℃）。4月13日该科研小组又有新发现：氟掺杂钐氧铁砷化合物假如在压力环境下产生作用，其超导临界温度可进一步提升至55 K（-218.15 ℃）。此外，中科院物理所闻海虎领导的科研小组还报告，锶掺杂镧氧铁砷化合物的超导临界温度为25 K（-248.15 ℃）^[4]，从此研究铁基超导体便在世界上形成一股热潮。引起许多科学家的兴趣的重要原因之一在于铁基超导体的结构与高温超导的铜氧平面类似，超导性发生在铁基平面上，属于二维的超导材料。因此尽管铁基超导体的临界温度只有数十开尔文，研究铁基超导体可能有助于了解高温超导的机制。

晶格结构

现有的铁基超导体从结构上可分为四类：（1111）、（122）、（111） 和 (11)。

氮磷族氧化物 (oxypnictide)	临界温度 (K)
LaO0.89F0.11FeAs	26[5]
LaO0.9F0.2FeAs	28.5[6]
CeFeAsO0.84F0.16	41[5]
SmFeAsO0.9F0.1	43[5]
La0.5Y0.5FeAsO0.6	43.1[7]
NdFeAsO0.89F0.11	52[5]
PrFeAsO0.89F0.11	52[8]
ErFeAsO1-y	45[9]
Al-32522 (CaAlOFeAs)	30(As), 16.6 (P)[10]
Al-42622 (CaAlOFeAs)	28.3(As), 17.2 (P)[11]
GdFeAsO0.85	53.5[12]
BaFe1.8Co0.2As2	25.3[13]
SmFeAsO~0.85	55[14]

非氮磷族氧化物 (non-oxypnictide)	临界温度 (K)
Ba0.6K0.4Fe2As2	38[15]
Ca0.6Na0.4Fe2As2	26[16]
CaFe0.9Co0.1AsF	22[17]
Sr0.5Sm0.5FeAsF	56[18]
LiFeAs	<18 [19] [20][21]
NaFeAs	9–25[22][23]
FeSe	<27[24][25]

参见

• 安德烈夫反射(Andreev reflection)
• 高温超导
• 近藤效应
• 磁化帆
• 氮磷族氧化物(oxypnictide)

参考文献

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