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2008

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T. Park;E. Park;Hanoh Lee;Tomasz Klimczuk;F. Ronning;J. D. Thompson

我们报道了CaFe_2As_2单晶的压力诱导超导性。在大气压下，这种材料在低于170 K时是反铁磁的，但在0.69 GPa的外加压力下变成超导的，转变温度Tc超过10 K。外加磁场对Tc的抑制率为−0。7 KT −1，给出外推的零温度上临界场为10 - 14 T。(Some本文中的数字仅为电子版中的彩色）四元ThCr 2Si 2晶体结构支持广泛的元素组合，仅Th位就被所有稀土元素、轻锕系元素、二价碱土元素Ca、Sr和Ba等占据。最近，在这种结构中形成的AFe 2As 2（A = Ca，Sr和Ba）材料[1]受到了新的关注[2 - 8]，因为它们与另一个化合物家族ROFeAs（其中R是稀土）相似，该化合物家族在四重ZrCuSiAs结构类型中结晶[9 - 14]。这两个系统都含有结构层的FeAs，在室温下进行四方晶系到正交晶系的转变，并支持反铁磁性的正交结构。面外层中的非等电子化学取代，例如，在BaFe 2As 2 [7 ]或Ff或Oin LaOFeAs [8]中用K取代Ba，引入额外的电荷载流子，抑制结构和磁性转变，并在数十开尔文的温度下诱导超导性。在这些不同的材料中，没有一种具有FeAs层的材料在没有电子掺杂的情况下是超导的，尽管名义上具有NiP层的等电子磷化镍BaNi 2 P2 [15]和LaONiP [16]在相对较低的温度（5 K）下确实超导。含磷化合物的晶胞体积小于其作为对应物，这表明，一个有效的化学压力取代作为较小的P原子可能会发挥重要作用。到目前为止，这些家族中还没有未掺杂的非超导成员

We report pressure-induced superconductivity in a single crystal of CaFe2As2. At atmospheric pressure, this material is antiferromagnetic below 170 K but under an applied pressure of 0.69 GPa becomes superconducting, with a transition temperature Tc exceeding 10 K. The rate of Tc suppression with applied magnetic field is −0. 7KT −1 , giving an extrapolated zero-temperature upper critical field of 10‐14 T. (Some figures in this article are in colour only in the electronic version) The tetragonal ThCr2Si2 crystal structure supports a wide range of elemental combinations, with the Th site alone being occupied by all the rare earths, the light actinides, divalent alkaline earths Ca, Sr and Ba and others. Recently, the AFe2As2 (A = Ca, Sr and Ba) materials that form in this structure [1] have received renewed attention [2‐8] due to their similarity to another family of compounds ROFeAs (where R is a rare earth) that crystallizes in the tetragonal ZrCuSiAs structure type [9‐14]. Both systems contain structural layers of FeAs, undergo a tetragonal to orthorhombic transition below room temperature and support antiferromagnetism in the orthorhombic structure. Non-isoelectronic chemical substitution in the out-of-plane layer, for example, substituting K for Ba in BaFe2As2 [7 ]o r Ff or Oi n LaOFeAs [8], introduces additional charge carriers, suppresses the structural and magnetic transitions, and induces superconductivity at temperatures in the tens of Kelvins. Of these various materials, none with FeAs layers is superconducting without electronic doping, though the nominally isoelectronic nickel phosphides, BaNi2P2 [15] and LaONiP [16], with NiP layers do superconduct at relatively low (5 K) temperatures. The unit cell volumes of the P-containing compounds are smaller than their As counterparts, and this suggests that an effective chemical pressure produced by replacing As with the smaller P atom may play a significant role. Thus far, no undoped, non-superconducting member of these families has

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