Polaritonic Probe of an Emergent 2D Dipole Interface

Abstract

The use of work-function-mediated charge transfer has recently emerged as a reliable route toward nanoscale electrostatic control of individual atomic layers. Using α-RuCl3 as a 2D electron acceptor, we are able to induce emergent nano-optical behavior in hexagonal boron nitride (hBN) that arises due to interlayer charge polarization. Using scattering-type scanning near-field optical microscopy (s-SNOM), we find that a thin layer of α-RuCl3 adjacent to an hBN slab reduces the propagation length of hBN phonon polaritons (PhPs) in significant excess of what can be attributed to intrinsic optical losses. Concomitant nano-optical spectroscopy experiments reveal a novel resonance that aligns energetically with the region of excess PhP losses. These experimental observations are elucidated by first-principles density-functional theory and near-field model calculations, which show that the formation of a large interfacial dipole suppresses out-of-plane PhP propagation. Our results demonstrate the potential utility of charge-transfer heterostructures for tailoring optoelectronic properties of 2D insulators.

Tunable Exciton Polaritons in Band-Gap Engineered Hexagonal Boron Nitride

“…22 On one hand, heterostructures are promising for tailoring optoelectronic properties of 2D insulators (such as hBN). 18 On the other hand, homostructures reveal quite interesting features, distinct from those of the initial isolated constituents. From the example of AB-stacking graphene bilayer, it was realized that a band gap can be opened and controlled electrostatically, using a voltage bias.…”

“…Such use allows to increase the mobility of charge carriers and produce well-defined (large quality factor Q ) electromagnetic (EM) resonances in polaritonic devices. Later, it became clear that hBN is interesting in its own right when light–matter interaction is considered. , The interaction with infrared radiation due to polar phonons in hBN gives rise to large- Q polaritonic resonances used for example in gas sensing . At the same time, the interaction of ultraviolet (UV) radiation with the electrons in hBN has promoted the field of UV photonics …”

“…2D materials can be combined by stacking several layers, forming van der Waals heterostructures; materials consisting of few layers have proven to be a fertile theoretical and experimental template for the study of unconventional physics . On one hand, heterostructures are promising for tailoring optoelectronic properties of 2D insulators (such as hBN) . On the other hand, homostructures reveal quite interesting features, distinct from those of the initial isolated constituents.…”