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arXiv 1402.3719cond-mat.str-elcond-mat.mes-hallcond-mat.mtrl-sci
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高电子密度SrTiO3量子阱中金属-绝缘体转变与结构畸变的相关性

Correlation between metal-insulator transitions and structural distortions in high-electron-density SrTiO3 quantum wells

Jack Y. Zhang, Clayton A. Jackson, Ru Chen, Santosh Raghavan, Pouya Moetakef, Leon Balents, Susanne Stemmer

摘要:

比较了SmTiO_3/SrTiO_3/SmTiO_3和GdTiO_3/SrTiO_3/GdTiO_3异质结构的电学和结构特性。这两种类型的结构都包含窄SrTiO 3量子阱,可容纳受限的高密度电子气。如前所示[Phys.Rev.B86,201102(R)(2012)],当嵌入GdTiO 3中的SrTiO 3量子阱的厚度减小时,它们显示出金属到绝缘体的转变,使得它们仅包含两个SrO层。相比之下,嵌入在SmTiO 3中的量子阱保持金属性,直到单个SrO层厚度。对称性降低的结构失真,通过量化的Sr柱位移,是存在于绝缘量子阱,但在所有的金属量子阱中是不存在或非常弱,独立于它们是否嵌入在SmTiO 3或Gd TiO 3。我们讨论的作用,正交畸变,轨道排序,和强电子相关性的过渡到绝缘状态。

英文摘要:

The electrical and structural characteristics of SmTiO3/SrTiO3/SmTiO3 and GdTiO3/SrTiO3/GdTiO3 heterostructures are compared. Both types of structures contain narrow SrTiO3 quantum wells, which accommodate a confined, high-density electron gas. As shown previously [Phys. Rev. B 86, 201102(R) (2012)] SrTiO3 quantum wells embedded in GdTiO3 show a metal-to-insulator transition when their thickness is reduced so that they contain only two SrO layers. In contrast, quantum wells embedded in SmTiO3 remain metallic down to a single SrO layer thickness. Symmetry-lowering structural distortions, measured by quantifying the Sr-column displacements, are present in the insulating quantum wells, but are either absent or very weak in all metallic quantum wells, independent of whether they are embedded in SmTiO3 or in GdTiO3. We discuss the role of orthorhombic distortions, orbital ordering, and strong electron correlations in the transition to the insulating state.

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