论文标题
由于退火而导致的电子状态的不同变化$ _ {1.8} $ eu $ _ {0.2} $ cuo $ _4 $和nd $ _ {2} $ cuo $ _4 $
Distinct variation of electronic states due to annealing in La$_{1.8}$Eu$_{0.2}$CuO$_4$ and Nd$_{2}$CuO$_4$
论文作者
论文摘要
我们进行了cu {\ it k} - ed x射线吸收良好的结构测量，对t'-type la $ _ {1.8} $ eu $ _ {0.2} $ cuo $ _4 $（leco）和nd $ _2 $ _2 $ cuo $ $ _4 $（nco）与Entrivient in eartiviation相关。 X射线吸收的X射线接近边缘结构光谱（AS）LECO与NCO的X射线吸收非常相似，表明AS T'-type Leco的基态是Mott的绝缘体。由于退火，我们发现了LECO的CU位点电子状态的显着变化。对超导LECO和非抗性NCO进行了退火后的电子密度（$ n _ {\ rm an} $），分别为每个Cu，分别为0.40和0.05电子。在LECO中，但在NCO中不进行，扩展的X射线吸收良好的结构分析显示，由于退火，Cu-O $ _2 $平面中Cu-O键的强度柔软，这与金属状态下对声子的筛选效果一致。由于LECO和NCO因退火而引起的氧损失的量是可以彼此可比的，因此这些结果表明两种化合物中的不同电子掺杂过程。 That electron-doping in NCO approximately follows the relation $n_{\rm AN}=2δ$ can be understood if electrons are doped through oxygen deficiency, but the anneal-induced metallic nature and large $n_{\rm AN}$ of LECO suggest a variation of the electronic band structure causes self-doping of carriers.与电荷转移缝隙的大小有关，讨论了由于退火而引起的掺杂过程差异的起源。
We performed Cu {\it K}-edge X-ray absorption fine structure measurements on T'-type La$_{1.8}$Eu$_{0.2}$CuO$_4$ (LECO) and Nd$_2$CuO$_4$ (NCO) to investigate the variation in the electronic state associated with the emergence of superconductivity due to annealing. The X-ray absorption near-edge structure spectra of as-sintered (AS) LECO are quite similar to those of AS NCO, indicating that the ground state of AS T'-type LECO is a Mott insulator. We found a significant variation of the electronic state at the Cu sites in LECO due to annealing. The electron density after annealing ($n_{\rm AN}$) was evaluated for both superconducting LECO and non-superconducting NCO and found to be 0.40 and 0.05 electrons per Cu, respectively. In LECO but not in NCO, extended X-ray absorption fine structure analysis revealed a softening in the strength of the Cu-O bond in the CuO$_2$ plane due to annealing, which is consistent with the screening effect on phonons in the metallic state. Since the amounts of oxygen loss due to annealing ($δ$) for LECO and NCO are comparable with each other, these results suggest distinct electron-doping processes in the two compounds. That electron-doping in NCO approximately follows the relation $n_{\rm AN}=2δ$ can be understood if electrons are doped through oxygen deficiency, but the anneal-induced metallic nature and large $n_{\rm AN}$ of LECO suggest a variation of the electronic band structure causes self-doping of carriers. The origin of the difference in doping processes due to annealing is discussed in connection with the size of the charge transfer gap.
