Surface conduction of topological Dirac electrons in bulk insulating Bi2Se3
Surface conduction of topological Dirac electrons in bulk insulating Bi2Se3
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DOI：
10.1038/nphys2286
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发表时间：
2012-06-01
期刊：
影响因子：
19.6
通讯作者：
Fuhrer, Michael S.
中科院分区：
文献类型：
--
作者：
Kim, Dohun;Cho, Sungjae;Fuhrer, Michael S.
新发现的三维强拓扑绝缘体（STIs）呈现出拓扑保护的狄拉克表面态（1,2）。尽管已经通过光谱学方法对STI表面态进行了研究，例如利用光发射（3 - 5）和扫描探针（6 - 10），但输运实验（11 - 17）未能证明STI最基本的特征：绝缘体态的拓扑表面中的双极性金属电子输运。在此我们表明，薄（约10纳米）、低掺杂的Bi₂Se₃（约10¹⁷ cm⁻³）晶体的表面具有强静电耦合，并且栅电极能够完全去除体态载流子，并使两个表面同时通过狄拉克点。我们观察到清晰的表面带传导，具有线性霍尔电阻率和明确的双极性场效应，以及电荷不均匀的最小电导率区域（18 - 20）。狄拉克带中电荷无序的理论（19 - 21）很好地解释了最小电导率（每个表面2到5 e²/h）以及剩余（ puddle，水坑状）载流子密度（0.4×10¹²到4×10¹² cm⁻²）的大小及其随无序强度的变化。从测量的载流子迁移率320 - 1500 cm² V⁻¹ s⁻¹，推断出带电杂质密度为0.5×10¹³到2.3×10¹³ cm⁻²。它们与零栅压下测量的掺杂水平（1×10¹³到3×10¹³ cm⁻²）大小相近，从而确定掺杂剂为带电杂质。
The newly discovered three-dimensional strong topological insulators (STIs) exhibit topologically protected Dirac surface states(1,2). Although the STI surface state has been studied spectroscopically, for example, by photoemission(3-5) and scanned probes(6-10), transport experiments(11-17) have failed to demonstrate the most fundamental signature of the STI: ambipolar metallic electronic transport in the topological surface of an insulating bulk. Here we show that the surfaces of thin (similar to 10 nm), low-doped Bi2Se3 (approximate to 10(17) cm(-3)) crystals are strongly electrostatically coupled, and a gate electrode can completely remove bulk charge carriers and bring both surfaces through the Dirac point simultaneously. We observe clear surface band conduction with a linear Hall resistivity and a well-defined ambipolar field effect, as well as a charge-inhomogeneous minimum conductivity region(18-20). A theory of charge disorder in a Dirac band(19-21) explains well both the magnitude and the variation with disorder strength of the minimum conductivity (2 to 5 e(2)/h per surface) and the residual (puddle) carrier density (0.4 x 10(12) to 4 x 10(12) cm(-2)). From the measured carrier mobilities 320-1,500 cm(2) V-1 s(-1), the charged impurity densities 0.5 x 10(13) to 2.3 x 10(13) cm(-2) are inferred. They are of a similar magnitude to the measured doping levels at zero gate voltage (1 x 10(13) to 3 x 10(13) cm(-2)), identifying dopants as the charged impurities.