Hyperbolic Dispersion Arising from Anisotropic Excitons in Two-Dimensional Perovskites
Hyperbolic Dispersion Arising from Anisotropic Excitons in Two-Dimensional Perovskites
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DOI：
10.1103/physrevlett.121.127401
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发表时间：
2018-09-19
影响因子：
8.6
通讯作者：
Schaller, Richard D.
中科院分区：
文献类型：
--
作者：
Guo, Peijun;Huang, Wei;Schaller, Richard D.
已知自由电子和光学声子的激发可以接近相对介电常数的负实部（ε<0），从而产生强的光-物质相互作用。然而，对激子产生的负ε'的研究却少得多。通过开发本文所述的基于介电涂层的技术，我们报告了由无机和有机亚晶格交替层组成的二维杂化钙钛矿（2DHP）的基本光学特性。 2DHP 的低成员（N = 1 和 N = 2）由于较大的激子结合能和相当大的振荡器强度而表现出负 epsilon'。此外，双曲色散（即 epsilon 随方向改变符号）发生在可见光范围内，这以前只能通过人造超材料实现。这种自然发生的奇异色散源于 2DHP 的极端各向异性激子行为，并且本质上可以支持大的光子态密度。我们认为其他几种范德华固体可能会表现出由激子响应引起的类似行为。
Excitations of free electrons and optical phonons are known to permit access to the negative real part of relative permittivities (epsilon' < 0) that yield strong light-matter interactions. However, negative epsilon' arising from excitons has been much less explored. Via development of a dielectric-coating based technique described herein, we report fundamental optical properties of two-dimensional hybrid perovskites (2DHPs), composed of alternating layers of inorganic and organic sublattices. Low members of 2DHPs (N = 1 and N = 2) exhibit negative epsilon' stemming from the large exciton binding energy and sizable oscillator strength. Furthermore, hyperbolic dispersion (i.e., epsilon' changes sign with directions) occurs in the visible range, which has been previously achieved only with artificial metamaterials. Such naturally occurring, exotic dispersion stems from the extremely anisotropic excitonic behaviors of 2DHPs, and can intrinsically support a large photonic density of states. We suggest that several other van der Waals solids may exhibit similar behaviors arising from excitonic response.