空穴掺杂镍基超导体（La $_{1-x}$ Sr $_{x}$）NiAsO的合成与表征
Synthesizing and characterization of hole doped nickel based superconductor (La$_{1-x}$Sr$_{x}$)NiAsO
摘要：
报道了空穴掺杂镍基超导体（$La_{1-x}Sr_{x})NiAsO$）的合成与表征。通过用Sr替代La，在掺杂水平x= 0.1 - 0.2时，超导转变温度$T_c$从母相$LaNiAsO$的2.4 K提高到3.7 K。$T_c$对空穴浓度的曲线显示出与电子掺杂样品$LaNiAs(O_{1-x}F_{x})$对称的行为。Ni基样品的正常态电阻率显示出良好的金属行为，并揭示了在150 K附近没有出现Fe基系统中出现的自旋密度波诱导的异常。霍尔效应测量表明，在$LaNiAsO$的母相中，电子传导主要由类电子载流子主导，而随着Sr掺杂量的增加，类空穴带将出现并最终占据主导地位，这种现象反映了$LaNiAsO$的费米面由电子袋和空穴袋组成，因此，一旦空穴袋的贡献超过电子袋的贡献，则载流子的符号可以改变。磁电阻测量和Kohler规则的违反进一步证明了多带效应主导（$La_{1-x}Sr_{x})NiAsO$）的正常态输运。
英文摘要：
We report the synthesizing and characterization of the hole doped Ni-based superconductor ($La_{1-x}Sr_{x})NiAsO$. By substituting La with Sr, the superconducting transition temperature $T_c$ is increased from 2.4 K of the parent phase $LaNiAsO$ to 3.7 K at the doping levels x= 0.1 - 0.2. The curve $T_c$ versus hole concentration shows a symmetric behavior as the electron doped samples $LaNiAs(O_{1-x}F_{x})$. The normal state resistivity in Ni-based samples shows a good metallic behavior and reveals the absence of spin density wave induced anomaly which appears in the Fe-based system at about 150 K. Hall effect measurements indicate that the electron conduction in the parent phase $LaNiAsO$ is dominated by electron-like charge carriers, while with more Sr doping, a hole-like band will emerge and finally prevail over the conduction, such a phenomenon reflects that the Fermi surface of $LaNiAsO$ comprises of electron pockets and hole pockets, thus the sign of charge carriers could be changed once the contribution of hole pockets overwhelms that of electron pockets. Magnetoresistance measurements and the violation of Kohler rule provide further proof that multiband effect dominate the normal state transport of ($La_{1-x}Sr_{x})NiAsO$.
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