Twistoptics: Manipulating Light-Matter Interactions at the Nanoscale with Twisted van der Waals Materials

Project Information

TWISTOPTICS

Grant agreement ID: 101044461

DOI

10.3030/101044461

EC signature date 30 September 2022

Start date 1 December 2022

End date 30 November 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 999 500,00

EU contribution

€ 1 999 500,00

Coordinated by

UNIVERSIDAD DE OVIEDO
Spain

Periodic Reporting for period 1 - TWISTOPTICS (Twistoptics: Manipulating Light-Matter Interactions at the Nanoscale with Twisted van der Waals Materials)

Reporting period: 2022-12-01 to 2025-05-31

Summary of the context and overall objectives of the project

van der Waals (vdW) materials are ideal platforms to host light at the nanoscale (nanolight) with unprecedented properties such as strong in-plane anisotropy, arbitrarily large momenta and high density of optical states, opening the door to develop planar optical nanodevices compatible with current on-chip technologies. Remarkably, the in-plane anisotropic propagation of nanolight can be steered by stacking two slabs of a vdW material rotated with respect to each other, resulting, for example, in canalization along one specific direction. Inspired by this breakthrough in nano-optics, which extends the exciting prospects of twistronics to the optics realm, this ERC project aims to develop the field of Twistoptics, where stacks of twisted layers of vdW materials enable unprecedented active control of light and light-matter interactions at the nanoscale. In a first stage, we will carry out a study of the most fundamental optical phenomena in Twistoptics - reflection and refraction of nanolight in twisted vdW structures-, and develop a technological platform that will enable active manipulation of nanolight via strain fields. In a second stage, we will make use of this knowledge and technological capabilities to design and fabricate functional nanodevices to explore directional strong coupling between nanolight and molecular vibrations, as well as inter-subband transitions in 2D semiconductors -in order to develop quantum Twistoptics. This proposal envisions the modification of material properties and dynamics at the nanoscale and the realization of efficient and compact sources of IR radiation and polaritons working at room temperature. These fundamental scientific advances will be of enormous relevance for the development of new nanotechnologies that will have a broad impact in various fields, such as molecular nano-sensing, quantum nanosciences, or nano-chemistry, where active control of fundamental light-matter processes at the nanoscale is of vital importance.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

-By fabricating reconfigurable twisted vdW trilayers, we have demonstrated the existence of multiple and spectrally robust photonic magic angles (Nature Materials 22 (7), 867-872, (2023)), which allow nanoscale polaritons to be guide (canalized) along desired directions in the plane.
-We have demonstrated a fundamentally new form of polariton propagation that emerges when twisting two anisotropic materials: unidirectional ray propagation, characterized by the absence of diffraction and the presence of a single phase of the propagating field (Álvarez-Cuervo et al. Nat. Comm. 15, 9042 (2024)). These polaritons appear if Twistoptics is combined with asymmetric stacking, i.e. when two anisotropic (hyperbolic) materials with very different layer thicknesses are stacked and twisted. In a large team effort, we experimentally demonstrated unidirectional ray polaritons in two complementary systems: a homostructure using two twisted α-MoO3 layers of very different thicknesses, and a heterostructure employing twisted α-MoO3 thin layers on-top of a β-Ga2O3 substrate. For both systems, we comprehensively study the physical mechanism of unidirectional ray polariton formation, to provide an intuitive physical understanding of the phenomenon.
- We theoretically introduced and experimentally demonstrated a novel PhPs canalization phenomenon taking place in α-MoO3/SiC twisted heterostructures. More importantly, we take advantage of this canalization to demonstrate the first proof-of-concept application based on this phenomenon: a lens capable of achieving super-resolution (~λ0/220) nanoimaging. Furthermore, the demonstrated imaging scheme transcends conventional projection limitations, allowing super-resolution images to be obtained at any desired location in the image plane. These results have been published in Duan et al. Science Advances ads0569 (2025).
- We theoretically propose and experimentally demonstrate by means of s-SNOM nano-imaging a novel polaritonic material platform based on single thin layers of α-MoO3 that allows for the efficient excitation of canalized polaritons. More importantly, these canalized polaritons exhibit unique properties such as a high density of optical states and a single well-defined propagating phase, conferring them a ray character (henceforth, ray polaritons). These results have been published in Terán-García et al. Nano Letters 10.1021/acs.nanolett.4c05277 (2025).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The work described in the previous sections are clear advances beyond the state of the art. In particular, the discovery of multiple magic angles in twisted trilayer structures and the finding of unidirectional ray polaritons can be considered advances in Twistoptics. In terms of applications, high directionality, tunability with frequency and twist angle, and long propagation lengths are ideal features for on-chip integration of waveguide, sensing, nanoimaging, as well as nanoscale thermal management. These results obtained for trilayers can be considered predicted or expected. However, the discovery of ray polaritons in asymmetric bilayer structures was quite unexpected, resulting from a fundamental analysis of interlayer coupling in stacks of polaritonic materials.

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