欠掺杂Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$，x=0.09和0.17自熔生长单晶的中子散射研究及三临界点的普适性
A neutron scattering study of the under-doped Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, x=0.09 and 0.17 self-flux grown single crystals and the universality of the tricritical point
摘要：
本文给出了欠掺杂超导Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$ x=0.17的零场和14.5 T的弹性中子散射测量以及零场和14 T的磁化强度测量的组合，以及在x=0.09的非超导晶体上的零场测量。数据表明，欠掺杂材料可能不是电子相分离的，而是具有略微不均匀的钾掺杂。在x=0.09的样品的转变下的磁序参数（OP）的温度依赖性比未掺杂的BaFe $_{2}$ As $_{2}$的情况下更平缓，这表明这种掺杂可能在三临界点附近。因此，我们提出三临界点是所有超导122的共同特征的假设。对于x=0.17的样品，当14 T的磁场将T $_{c}$从$\approx$ 17 K抑制到$\approx$ 8 K时，1.2 K处的磁布拉格峰（1 0 3）的强度增强了10 $%$，显示出超导性（SC）和反铁磁性（AFM）的竞争.在（T $_{c}$，T $_{N}$）温度区间内的磁布拉格峰（1 0 3）的强度在14.5 T下在10 $%$的统计误差内几乎保持不变。目前的结果进行了讨论的背景下，现有的文献。
英文摘要：
We present a combination of elastic neutron scattering measurements in zero and 14.5 T and magnetization measurements in zero and 14 T on under-doped superconducting Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ x=0.17, and the same measurements in zero field on a non-superconducting crystal with x=0.09. The data suggest that the under-doped materials may not be electronic phase separated but rather have slightly inhomogeneous potassium doping. The temperature dependence of the magnetic order parameter (OP) below the transition of the sample with x=0.09 is more gradual than that for the case of the un-doped BaFe$_{2}$As$_{2}$, suggesting that this doping may be in the vicinity of a tricritical point. We advance therefore the hypothesis that the tricritical point is a common feature of all superconducting 122s. For the x=0.17 sample, while T$_{c}$ is suppressed from $\approx$17 K to $\approx$8 K by a magnetic field of 14 T, the intensity of the magnetic Bragg peaks (1 0 3) at 1.2 K is enhanced by 10$%$ showing competition of superconductivity (SC) and antiferromagnetism (AFM). The intensity of the magnetic Bragg peaks (1 0 3) in the (T$_{c}$, T$_{N}$) temperature interval remain practically unchanged in 14.5 T within a 10$%$ statistical error. The present results are discussed in the context of the existing literature.
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