美国哥伦比亚大学A. J. Sternbach研究小组报道了双曲异质双晶体中的负折射。该项研究成果发表在2023年2月10日出版的《科学》上。

该研究组看到了声子极化激元的负折射，它发生在两个天然晶体之间的界面上。极化激元——红外光子和晶格振动的混合体——形成的准直射线在穿过两种双曲范德华材料(氧化钼(MoO₃)和同位素纯六方氮化硼(h¹¹BN))之间的晶面界面时显示出负折射。在一个特殊的频率ω₀上，这些射线可以沿着封闭的菱形轨迹循环。

研究人员已经证明，极化激元本征模显示出了被多个能隙中断的正色散和负色散区域，这主要是由极化激元能级排斥和强耦合产生的。

附：英文原文

Title: Negative refraction in hyperbolic hetero-bicrystals

Author: A. J. Sternbach, S. L. Moore, A. Rikhter, S. Zhang, R. Jing, Y. Shao, B. S. Y. Kim, S. Xu, S. Liu, J. H. Edgar, A. Rubio, C. Dean, J. Hone, M. M. Fogler, D. N. Basov

Issue&Volume: 2023-02-10

Abstract: We visualized negative refraction of phonon polaritons, which occurs at the interface between two natural crystals. The polaritons—hybrids of infrared photons and lattice vibrations—form collimated rays that display negative refraction when passing through a planar interface between the two hyperbolic van der Waals materials: molybdenum oxide (MoO3) and isotopically pure hexagonal boron nitride (h11BN). At a special frequency ω0, these rays can circulate along closed diamond-shaped trajectories. We have shown that polariton eigenmodes display regions of both positive and negative dispersion interrupted by multiple gaps that result from polaritonic-level repulsion and strong coupling.

DOI: adf1065

Source: https://www.science.org/doi/10.1126/science.adf1065