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arXiv 0806.1315cond-mat.mtrl-sci
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SrRuO块体和薄膜$_3$的电子性质:金属-绝缘体转变的研究

Electronic properties of bulk and thin film SrRuO$_3$: a search for the metal-insulator transition

James M. Rondinelli, Nuala M. Caffrey, Stefano Sanvito, Nicola A. Spaldin

摘要:

我们计算的4 $d$铁磁体SrRuO $_3$在散装和薄膜形式的性质,目的是了解实验观察到的金属到绝缘体的转变,在减少厚度。虽然4个$d$轨道的空间范围相当大,但许多实验结果表明,电子-电子相关性在确定这种材料的电子结构中起着重要作用。为了研究关联的重要性,我们使用了两种超越传统的局域密度近似的密度泛函理论:局域自旋密度近似+ Hubbard $U$(LSDA+ $U$)和赝势自相互作用修正(pseudo-SIC)方法。我们发现,与LSDA预测的电子结构的细节不同意与实验光谱数据为体和薄膜SrRuO $_3$。改进发现,包括电子-电子的相关性,我们认为,体正交SrRuO $_3$是一个{ \it弱强相关}铁磁体,其电子结构是最好的描述由0.6 eV的现场哈伯德项,或等效的自相互作用误差的校正。我们还执行{ \it从头计算}运输计算,确认SrRuO $_3$具有负自旋极化在费米能级,由于少数Ru 4 $d$带中心的位置。即使在我们的计算中包含的相关性,我们无法重现实验观察到的金属-绝缘体转变,这表明SrRuO $_3$超薄膜的电子行为可能是由外在因素,如表面无序和缺陷。

英文摘要:

We calculate the properties of the 4$d$ ferromagnet SrRuO$_3$ in bulk and thin film form with the aim of understanding the experimentally observed metal to insulator transition at reduced thickness. Although the spatial extent of the 4$d$ orbitals is quite large, many experimental results have suggested that electron-electron correlations play an important role in determining this material's electronic structure. In order to investigate the importance of correlation, we use two approaches which go beyond the conventional local density approximation to density functional theory (DFT): the local spin density approximation + Hubbard $U$ (LSDA+$U$) and the pseudopotential self-interaction correction (pseudo-SIC) methods. We find that the details of the electronic structure predicted with the LSDA do not agree with the experimental spectroscopic data for bulk and thin film SrRuO$_3$. Improvement is found by including electron-electron correlations, and we suggest that bulk orthorhombic SrRuO$_3$ is a {\it weakly strongly-correlated} ferromagnet whose electronic structure is best described by a 0.6 eV on-site Hubbard term, or equivalently with corrections for the self-interaction error. We also perform {\it ab initio} transport calculations that confirm that SrRuO$_3$ has a negative spin polarization at the Fermi level, due to the position of the minority Ru 4$d$ band center. Even with correlations included in our calculations we are unable to reproduce the experimentally observed metal-insulator transition, suggesting that the electronic behavior of SrRuO$_3$ ultra-thin films might be dominated by extrinsic factors such as surface disorder and defects.

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