Simultaneous spin-state-insulatormetal transition in Pr 0.5Ca 0.5CoO 3
Simultaneous spin-state-insulatormetal transition in Pr 0.5Ca 0.5CoO 3
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Pr 0.5Ca 0.5CoO 3 中同时自旋态-绝缘体金属转变
DOI：
10.1016/j.elspec.2005.01.225
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
K. Shimada
中科院分区：
文献类型：
--
作者：
T. Saitoh;Y. Yamashita;Nobutoshi Todoroki;T. Kyōmen;M. Itoh;Mitsuharu Higashiguchi;M. Nakatake;K. Shimada
LaCoO{sub 3}在100 K附近的温度诱导顺磁性一直被认为是该化合物的特征现象，但对其解释尚未确定。一个原因是低自旋（LS）基态和其他中间自旋（IS）或高自旋（HS）态不能完全解析，因为这些态通过热激发填充。在这里，我们提出了一个明显的变化，由于纯的LS-IS过渡的Co氧化物的电子结构的第一个观察; Pr{sub 0.5}Ca{sub 0.5}CoO{sub 3}表现出同时的LS-IS和绝缘体-金属一级相变约90 K随温度的升高。由于跃迁的一阶性质，IS相不被热激发填充，这使得我们能够独立地研究LS-和IS-Co 3d态的电子结构。图1显示了Pr{sub 0.5}Ca{sub 0.5}CoO{sub 3}的温度依赖性光电发射光谱。在70 ~ 100 K温度范围内，Co的3dt 2g态的A峰被迅速抑制。与理论计算结果相比，这种变化应该代表LS到IS的自旋态跃迁。观察到的“纯”LS和IS光谱之间的变化将排除LaCoO{sub 3}中的简单LS-HS方案，因此证明了IS状态在激发态和载流子掺杂区中的重要性。
The temperature-induced paramagnetism in LaCoO{sub 3} around 100 K has long been known as a characteristic phenomenon of this compound, but its interpretation is not settled yet. One reason is that the low-spin (LS) ground state and other intermediate-spin (IS) or high-spin (HS) states cannot be resolved completely because such states are populated by thermal excitation. Here we present a first observation of a distinct change in the electronic structure due to a pure LS-IS transition of a Co oxide; Pr{sub 0.5}Ca{sub 0.5}CoO{sub 3} exhibits a simultaneous LS-IS and insulator-metal first-order phase transition around 90 K with increasing temperature. Because of the first- order nature of the transition, the IS phase is not populated by thermal excitation, which enables us to investigate the electronic structure of the LS- and IS-Co 3d states, independently. Figure 1 shows temperature-dependent photoemission spec- tra of Pr{sub 0.5}Ca{sub 0.5}CoO{sub 3}. The leading peak A, which is Co 3d t 2g states, is rapidly suppressed from 70 K to 100 K. Compared with a theoretical calculation, this change should be representing the LS to IS spin-state transition. The observed change between the 'pure' LS and IS spectra will exclude the simple LS-HS scenario in LaCoO{sub 3} and hence demonstrates the importance of the IS state in both excited states and the carrier-doped region.