Observation of Dirac plasmons in a topological insulator
Observation of Dirac plasmons in a topological insulator
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DOI：
10.1038/nnano.2013.134
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发表时间：
2013-08-01
影响因子：
38.3
通讯作者：
Lupi, S.
中科院分区：
文献类型：
--
作者：
Di Pietro, P.;Ortolani, M.;Lupi, S.
等离子体激元是电子的量子化集体振荡，已在金属和掺杂半导体中观察到。普通大质量电子的等离子体激元长期以来一直是等离子体激元和光学超材料研究的基本成分(1)。然而，最近才在纯二维电子系统石墨烯中观察到无质量狄拉克电子的等离子体激元(2)。它们的特性对于太赫兹和中红外频率范围内的新型可调谐等离子体超材料很有前景(3)。由于绝缘体相中存在强自旋轨道相互作用，狄拉克费米子也出现在拓扑绝缘体表面形成的二维电子气中 (4)。因此，人们可以使用红外光谱来寻找它们的集体激发。在这里，我们报告了拓扑绝缘体（Bi2Se3）中等离子体激发的第一个实验证据。该材料被制备成不同宽度W和周期2W的薄微带阵列，以选择合适的等离激元波矢k值。研究发现等离子激元的线宽在 6 K 至 300 K 之间的温度下几乎保持恒定，正如激发拓扑载流子时所预期的那样。此外，通过改变 W 并测量太赫兹范围内的等离子体激元频率与 k 的关系，我们表明，在不使用任何拟合参数的情况下，色散曲线与狄拉克等离子体激元的预测在数量上一致。
Plasmons are quantized collective oscillations of electrons and have been observed in metals and doped semiconductors. The plasmons of ordinary, massive electrons have been the basic ingredients of research in plasmonics and in optical metamaterials for a long time(1). However, plasmons of massless Dirac electrons have only recently been observed in graphene, a purely two-dimensional electron system(2). Their properties are promising for novel tunable plasmonic metamaterials in the terahertz and mid-infrared frequency range(3). Dirac fermions also occur in the two-dimensional electron gas that forms at the surface of topological insulators as a result of the strong spin-orbit interaction existing in the insulating bulk phase(4). One may therefore look for their collective excitations using infrared spectroscopy. Here we report the first experimental evidence of plasmonic excitations in a topological insulator (Bi2Se3). The material was prepared in thin micro-ribbon arrays of different widths W and periods 2W to select suitable values of the plasmon wavevector k. The linewidth of the plasmon was found to remain nearly constant at temperatures between 6 K and 300 K, as expected when exciting topological carriers. Moreover, by changing W and measuring the plasmon frequency in the terahertz range versus k we show, without using any fitting parameter, that the dispersion curve agrees quantitatively with that predicted for Dirac plasmons.