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钙钛矿锰氧化物中的极化子研究
Investigation of polarons in perovskite manganites
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摘要: 钙钛矿锰氧化物（以下简称锰氧化物，如La1-xSrxMnO3等，X为掺杂浓度）因其优异的电、磁性质受到人们广泛的关注，但是对于其材料内部载流子性质的认识至今仍没有统一定论．本文基于锰氧化物内Mn—O链的特点，建立一维紧束缚模型，对锰氧化物载流子的性质展开研究．发现在掺杂浓度X=0．5时，系统处于铁磁态，自旋能级完全劈裂，价带和导带之间存在带隙，所有电子态呈现扩展行为．进一步掺杂，将出现局域电子态，同时伴随着晶格的局域畸变，形成所谓的极化子．伴随着极化子的出现，带隙中出现极化子深能级．极化子携带的电荷量越多，形成的晶格缺陷越深，局域能级也越深．当极化子的电荷量继续增加时，极化子解离，载流子倾向于形成能量更低的正反“孤子”对．Abstract: Perovskite manganites have aroused a great interest in their outstanding electrical and magnetic properties, but the characteristics of carders in these materials are still under debate. According to the Mn---O chain, we build a one-dimensional tight-binding model to study the characteristics of charge carders in manganites. It is obtained that at doping concentration :r = 0.5, the system shows a ferromagnetic state and the energy bands of spin up and spin down are completely splitted. A gap exists between valence band and conduction band, and all the electronic states are extended. With further doping, a localized electronic state appears, which we call a polaron. Accompanied with the electronic state, local distortions of the lattice and deep levels appear in the gap. The depth of the polaron increases with the doping quantity of electrons. It is also found that the polaron is spin polarized and has a maximum electronic charge of 0.621 e in the present parameters, beyond which the polaron will be divided into two separate states called solitons.
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