Anisotropic thermodynamic and transport properties of single-crystalline Ba1-xKxFe2As2 (x=0 and 0.45)
Anisotropic thermodynamic and transport properties of single-crystalline Ba1-xKxFe2As2 (x=0 and 0.45)
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DOI：
10.1103/physrevb.78.014507
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发表时间：
2008-07-01
影响因子：
3.7
通讯作者：
Canfield, P. C.
中科院分区：
文献类型：
--
作者：
Ni, N.;Bud'ko, S. L.;Canfield, P. C.
用1%或更少的溶剂从过量Sn中生长出BaFe_2As_2和Ba_（0.55）K_（0.45）Fe_2As_2单晶。晶体是非常云母的，很容易剥落，尺寸可以大到3x3x0.2 mm（3）。BaFe_2As_2单晶在85 K附近出现了从高温四方相到低温正交相的结构相变，在1.8 K以下没有表现出超导性。这种转变可以在电阻率、霍尔电阻率、比热和各向异性磁化率中检测到。在Ba_（0.55）K_（0.45）Fe_（2As）_2单晶中，这种转变被抑制，而在接近30 K的转变温度下出现超导性。虽然超导转变很容易在电阻率和磁化强度测量中检测到，但在T-c附近比热的变化很小，但可以分辨，使Δ C-p/γ T-c近似为1。当沿着c轴施加时，施加140 kOe的磁场抑制Tc，其值仅与4 K相似，而当垂直于c轴施加时，其值与2 K相似。各向异性上临界场的比率，γ =H-c2（垂直于c）/H-c2（平行于c），在2.5和3.5之间变化的温度下降到类似的2 K低于T-c。
Single crystals of BaFe2As2 and Ba0.55K0.45Fe2As2 have been grown out of excess Sn with 1% or less incorporation of solvent. The crystals are exceptionally micaceous, are easily exfoliated, and can have dimensions as large as 3x3x0.2 mm(3). The BaFe2As2 single crystals manifest a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase near 85 K and do not show any sign of superconductivity down to 1.8 K. This transition can be detected in the electrical resistivity, Hall resistivity, specific heat, and the anisotropic magnetic susceptibility. In the Ba0.55K0.45Fe2As2 single crystals this transition is suppressed and instead superconductivity occurs with a transition temperature near 30 K. Whereas the superconducting transition is easily detected in resistivity and magnetization measurements, the change in specific heat near T-c is small, but resolvable, giving Delta C-p/gamma T-c approximate to 1. The application of a 140 kOe magnetic field suppresses T-c by only similar to 4 K when applied along the c axis and by similar to 2 K when applied perpendicular to the c axis. The ratio of the anisotropic upper critical fields, gamma=H-c2(perpendicular to c)/H-c2(parallel to c), varies between 2.5 and 3.5 for temperatures down to similar to 2 K below T-c.