Doping-driven topological polaritons in graphene/α-MoO3 heterostructures

Abstract

Control over charge carrier density provides an efficient way to trigger phase transitions and modulate the optoelectronic properties of materials. This approach can also be used to induce topological transitions in the optical response of photonic systems. Here we report a topological transition in the isofrequency dispersion contours of hybrid polaritons supported by a two-dimensional heterostructure consisting of graphene and α-phase molybdenum trioxide. By chemically changing the doping level of graphene, we observed that the topology of polariton isofrequency surfaces transforms from open to closed shapes as a result of doping-dependent polariton hybridization. Moreover, when the substrate was changed, the dispersion contour became dominated by flat profiles at the topological transition, thus supporting tunable diffractionless polariton propagation and providing local control over the optical contour topology. We achieved subwavelength focusing of polaritons down to 4.8% of the free-space light wavelength by using a 1.5-μm-wide silica substrate as an in-plane lens. Our findings could lead to on-chip applications in nanoimaging, optical sensing and manipulation of energy transfer at the nanoscale.

Gate-tunable negative refraction of mid-infrared polaritons

“…S1). By contrast, graphene supports highly confined isotropic plasmons in this spectral region ( 29 , 30 ), such that anisotropic hyperbolic PhPs in the α-MoO 3 couple to graphene plasmons and results in an optical topological transition that allows us to flexibly engineer dispersion and isofrequency contours (IFCs) ( 31 – 34 ) (fig. S2).…”

Perspective on Meta-Boundaries

“…Remarkably, this kind of multiple meta-boundaries can support the emergence of excitonic superfluid phase . Moreover, the out-of-plane interaction between neighboring meta-boundaries would become more complex, if there exists the interlayer twist angle, − as schematically shown in Figure e. For example, Figure f shows the multiple meta-boundaries composed of rotated multiple bilayer graphene .…”

Near-field optical characterization of atomic structures and polaritons in twisted two-dimensional materials

“…Zeng 等人通过模拟计算发现在石墨烯和 α-MoO 3 堆叠的异质界面结构中， 调节石 墨烯费米能级和 α-MoO 3 的厚度分别可以实现杂化极化激元的椭圆和双曲线之间 的转变 [84] 。同年，Hai Hu 等人在实验上实现了通过改变费米能来调控"石墨烯 /α-MoO 3 /衬底" 结构的极化激元的拓扑转变 [85] 。 该团队还发现， 在红外光 910 cm -1 的波数下，石墨烯/α-MoO 3 结构在 Au 衬底上比在 SiO 2 衬底上更容易实现调控， 即更低的费米能即可实现双曲线到椭圆的极化激元的转变。 图 10 转角双层 α-MoO 3 的声子极化激元的拓扑转变。 [83] (f-i)和(n-q)对应计算的电场分布 z 分量的实数部分，Re(Ez)。(出自文献 [83] ，已获得 授权)…”