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arXiv 1502.04677cond-mat.mes-hall
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极性异质结自旋轨道控制的量子电容

Spin-orbit controlled quantum capacitance of a polar heterostructure

Kevin Steffen, Florian Loder, Thilo Kopp

摘要:

具有极性膜的氧化物异质结构显示出特殊的电子性质,例如在其内部界面处的电子重构和二维金属态的形成。此外,来自极性层的电场是反转对称性破缺的,并在界面电子系统中产生Rashba自旋轨道耦合(RSOC)。我们研究了异质结构的量子电容,其中金属界面处的相当大的RSOC由表面电极的电场控制。这种结构例如由SrTiO_3衬底上的LaAlO_3膜给出,其由顶部电极选通。这样的异质结构可以表现出其电容的强烈增强[Li等人,Science 332,825(2011)]。电容与异质结构的电子可压缩性有关,但两者并不等价。事实上,电荷转移到界面控制电容和压缩性之间的关系。我们发现,由于一个强大的RSOC,量子电容可以大于经典的几何值。然而,与最近的研究结果相反[Caprara等人,物理修订版信函109,196401(2012); Bucheli等人,Phys.Rev.B89,195448(2014); Seibold等人,欧罗巴Lett. 109,17006(2015)]的压缩性并没有成为负的实际参数值的LaAlO_3/SrTiO_3,因此,我们发现,没有相分离状态诱导的强RSOC在这些界面。

英文摘要:

Oxide heterostructures with polar films display special electronic properties, such as the electronic reconstruction at their internal interfaces with the formation of two-dimensional metallic states. Moreover, the electrical field from the polar layers is inversion-symmetry breaking and generates a Rashba spin-orbit coupling (RSOC) in the interfacial electronic system. We investigate the quantum capacitance of a heterostructure in which a sizeable RSOC at a metallic interface is controlled by the electric field of a surface electrode. Such a structure is, for example, given by a LaAlO_3 film on a SrTiO_3 substrate which is gated by a top electrode. Such heterostructures can exhibit a strong enhancement of their capacitance [Li et al., Science 332, 825 (2011)]. The capacitance is related to the electronic compressibility of the heterostructure, but the two quantities are not equivalent. In fact, the transfer of charge to the interface controls the relation between capacitance and compressibility. We find that due to a strong RSOC, the quantum capacitance can be larger than the classical geometric value. However, in contrast to the results of recent investigations [Caprara et al., Phys. Rev. Lett. 109, 196401 (2012); Bucheli et al., Phys. Rev. B 89, 195448 (2014); Seibold et al., Europhys. Lett. 109, 17006 (2015)] the compressibility does not become negative for realistic parameter values for LaAlO_3/SrTiO_3 and, therefore, we find that no phase-separated state is induced by the strong RSOC at these interfaces.

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