Weak localization of bulk channels in topological insulator thin films
Weak localization of bulk channels in topological insulator thin films
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DOI：
10.1103/physrevb.84.125138
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发表时间：
2011-09-29
影响因子：
3.7
通讯作者：
Shen, Shun-Qing
中科院分区：
文献类型：
--
作者：
Lu, Hai-Zhou;Shen, Shun-Qing
当强自旋 - 轨道耦合或散射起作用时，预计会出现弱反局域化（WAL）。拓扑绝缘体体态中的自旋 - 轨道耦合非常强，足以导致拓扑相变。然而，最近在拓扑绝缘体中观察到的弱反局域化似乎其源于体态的原因并不明确。从三维拓扑绝缘体的有效模型出发，我们发现拓扑绝缘体薄膜的最低二维（2D）体子带可以用修正的有质量狄拉克模型来描述。我们推导出了二维体子带和表面带的磁导率公式。由于能隙相对较大，二维体子带可能处于也预期会出现幺正行为甚至弱局域化（WL）的区域，而不总是弱反局域化。因此，体态可能对磁导率贡献较小，甚至抵消来自表面态的弱反局域化。当体态弱局域化通道数量超过表面弱反局域化通道时，磁导率曲线可能会出现拐点，这为体态的弱局域化提供了一个特征。
Weak antilocalization (WAL) is expected whenever strong spin-orbit coupling or scattering comes into play. Spin-orbit coupling in the bulk states of a topological insulator is very strong, enough to result in the topological phase transition. However, the recently observed WAL in topological insulators seems to have an ambiguous origin from the bulk states. Starting from the effective model for three-dimensional topological insulators, we find that the lowest two-dimensional (2D) bulk subbands of a topological insulator thin film can be described by the modified massive Dirac model. We derive the magnetoconductivity formula for both the 2D bulk subbands and surface bands. Because with relatively large gap, the 2D bulk subbands may lie in the regimes where the unitary behavior or even weak localization (WL) is also expected, instead of always WAL. As a result, the bulk states may contribute small magnetoconductivity or even compensate the WAL from the surface states. Inflection in magnetoconductivity curves may appear when the bulk WL channels outnumber the surface WAL channels, providing a signature of the weak localization from the bulk states.