通过带有超近反射器的金属接触二维系统实现完美吸收
Perfect absorption by metal-contacted two-dimensional systems with ultra-proximate reflectors
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中文总结 AI 辅助
该研究提出一种由窄二维区域与宽金属区域构成的周期结构，通过超近反射器实现二维系统的100%完美吸收，其共振无需依赖高电子迁移率。
中文摘要 AI 辅助
大多数二维电子系统的电磁吸光度通常远低于1，这既阻碍了其在光电探测中的实际应用，也限制了对其光学性质的基础研究。本文展示了一种由窄二维区域与宽完美导电金属区域连接构成的周期结构可实现高吸光度：当二维系统的填充因子f等于其无量纲电导率η=σZ₀/2（Z₀为自由空间阻抗）时，吸光度可达50%；若将该周期结构置于完美导电电磁反射器上方且满足f=2η，吸光度可进一步提升至100%。令人惊讶的是，二维系统与反射器之间的最优距离可远低于光学中传统吸收增强条件假设的入射波长λ₀的四分之一；对于低填充因子f≪1、衬底介电常数大且光栅周期与λ₀相当的情况，该最优距离趋于零。当光栅几何参数超过临界值时，吸光度最大值不再存在，临界行为表现为纯实电导率的“脏”二维系统中的大幅共振，而载流子动量弛豫时间的增加会降低该共振峰，这种共振虽模拟了等离子体共振，但不依赖高电子迁移率。
英文摘要
Electromagnetic absorbance by most two-dimensional electron systems is typically well below unity, which hinders both practical applications in photodetection and fundamental studies of their optical properties. Here, we show that a periodic structure comprised of narrow two-dimensional sections connected with wide perfectly conducting metal sections enables large absorbance. It reaches 50 \% provided the filling factor by the two-dimensional system $f$ equals its dimensionless conductivity $η=σZ_0/2$, where $Z_0$ is the free-space impedance. The absorbance is further raised to 100 \% if the periodic structure is placed above a perfectly conducting electromagnetic reflector, and provided $f=2η$. Surprisingly, the optimal distance between two-dimensional system and reflector may fall well below the quarter of incident wavelength $λ_0/4$, which was assumed as conventional absorption enhancement condition in optics. For low filling factors $f\ll1$, large dielectric constants of the substrate, and grating periods comparable with $λ_0$, the optimal distance to reflector tends to zero. Above the critical values of the grating geometrical parameters, the absorbance maximum ceases to exist. The critical behavior manifests as a large-amplitude resonance in 'dirty' two-dimensional system with purely real conductivity, while enhancement of carrier momentum relaxation time lowers the resonant peak. Such resonance mimics the plasmonic one, but does not rely on high electron mobility.
