论文标题
正方形平面环境中Ni $^{2+} $的巨型轨道极化
Giant orbital polarization of Ni$^{2+}$ in square planar environment
论文作者
论文摘要
了解Ni $^{2+} $在氧气平面环境中的电子行为是揭示最近在孔掺杂的镍液中脱离镍nd $ _ {0.8} $ _ {0.8} $ sr $ _ {0.2} $ nio $ _2 $ _2 $ _2 $的关键。为了确定镍和铜酸盐超导性之间的主要相似性/差异，在相同的正方形平面环境中对Ni $^{2+} $和Cu $^{2+} $的电子结构的研究是必不可少的。为了解决这些问题，我们研究了SR $ _2 $ CUO $ _3 $的电子结构和Ni掺杂的Sr $ _2 $ CUO $ _3 $包含（Cu/Ni）O $ $ _4 $方形平面单元的单晶。我们在SR $ _2 $ _2 $ _2 $ _ {0.9} $ ni $ _ {0.1} $ o $ $ _3 $中的Ni中的X射线吸收光谱实验揭示了非常大的轨道偏光，这是高$ T_C $ Cuprate的特征。这是由于低旋转$ s $ = 0配置而引起的，在Ni 3 $ d_ {x^2 -y^2} $ orbitals中，与预期的高旋转$ s $ = 1状态相反。这样的$ S $ = 0 ni $^{2+} $在孔掺杂的镍中的存在与张米单线类似。但是，与高$ t_c $ cuprates相比，Nio $ _4 $单位的Mott Hubbard绝缘性质将指向镍的不同电子相位空间。
Understanding the electronic behavior of Ni$^{2+}$ in a square planar environment of oxygen is the key to unravel the origin of the recently discovered superconductivity in the hole doped nickelate Nd$_{0.8}$Sr$_{0.2}$NiO$_2$. To identify the major similarities/dissimilarities between nickelate and cuprate superconductivity, the study of the electronic structure of Ni$^{2+}$ and Cu$^{2+}$ in an identical square planar environment is essential. In order to address these questions, we investigate the electronic structure of Sr$_2$CuO$_3$ and Ni doped Sr$_2$CuO$_3$ single crystals containing (Cu/Ni)O$_4$ square planar units. Our polarization dependent X-ray absorption spectroscopy experiments for Ni in Sr$_2$Cu$_{0.9}$Ni$_{0.1}$O$_3$ have revealed very large orbital polarization, which is a characteristic feature of high $T_c$ cuprate. This arises due to the low spin $S$=0 configuration with two holes in Ni 3$d_{x^2-y^2}$ orbitals - in contrast to the expected high spin $S$=1 state from Hund's first rule. The presence of such $S$=0 Ni$^{2+}$ in hole doped nickelate would be analogous to the Zhang Rice singlet. However, the Mott Hubbard insulating nature of the NiO$_4$ unit would point towards a different electronic phase space of nickelates, compared to high $T_c$ cuprates.
