Microcavity polaritons in atomically thin semiconductors and heterostructures: many-body and nonlinear phenomena

Lead Research Organisation: University of Sheffield
Department Name: Physics and Astronomy

Abstract

Atomically thin materials offer a new paradigm for control of electronic excitations in the extreme two-dimensional (2D) limit in condensed matter. Recently this concept has been developed further when artificial potentials for electrons were created in heterostructures consisting of stacked 2D layers held together by van der Waals forces, and light was used to access and manipulate electronic spin and valley degrees of freedom in atomically-thin semiconducting transition metal dichalcogenides (TMDCs). A significant world-wide effort in the last 5 years has resulted in intense studies of optical properties of TMDC atomic layers in the linear regime. Here, we propose to use this new class of (2D) semiconducting crystals to demonstrate unexplored approaches to exploiting nonlinear optical phenomena on the nano-scale in regimes unattainable by other ultra-fast photonic materials. To achieve this, we will exploit robust excitonic complexes observable up to room T, which will be generated and controlled in artificially created vertical stacks of 2D atomic layers. Giant nonlinearities enabling ultra-fast control of light with light of low intensity will be realised and explored in such van der Waals heterostructures placed in optical microcavities, operating in the strong light-matter coupling regime that we demonstrated recently. In this regime part-light-part-matter polaritons are formed, with the exciton part responsible for the strong nonlinearity and the photon part providing efficient coupling to light. This work will open a new route to development of highly nonlinear nano-photonic devices such as miniature ultra-fast modulators and switches, with high potential to impact on a new generation of signal processing and quantum technology hardware.

Planned Impact

Our Impact strategy will have four main components:

1. Knowledge dissemination within the scientific community outside the consortium will be achieved via publications in leading journals including Nature family and Science; talks at international conferences and workshops; participation in large-scale initiatives including (i) the European Graphene Flagship, (ii) Sir Henry Royce Institute for Advanced Materials (SHRI), (iii) National Graphene Institute (NGI), (iv) Horizon-2020 Spin-NANO Marie Sklodowska-Curie ITN, (v) ERC Synergy grant Hetero2D, (vi) EPSRC Engineering Grand Challenges grant 'Engineering van der Waals heterostructures: from atomic level layer-by-layer assembly to printable innovative devices' (EP/N010345/1).

2. Knowledge and technology transfer and direct engagement with industry. Our project concerns fundamental research into 2D materials with a strong potential to impact development of nonlinear optical devices for novel photonic integrated circuits, miniature and energy efficient active photonic elements, which are conceptually essential for future development in telecommunications and may also be used in a long-run to boost speed in supercomputers. At this early stage in the exploration of fundamental properties of 2D materials, our industrial engagement strategy will consist of establishing and maintaining long-lasting contacts with relevant industry. This will be achieved by providing the flow of information between our project and industry, as well as directly engaging with several industrial partners: Helia Photonics, Attocube Systems and HQGraphene. It is important to emphasize that this consortium has already established extremely reliable routes for engagement with industry: we will connect with industry via the national and international hubs and large-scale projects (i)-(vi) above, all addressing 2D materials. These multi-lateral initiatives and projects are intrinsically designed to encourage interaction between academics and industry.

3. Training of highly qualified personnel. We aim to train 4 postdoctoral researchers and 3 PhD students to high levels in physics, optics, theoretical analysis and device fabrication during the course of the grant. All these topical areas are highly relevant industrially and academically. The training in professional skills both in Sheffield and Manchester will be supplemented by attendance at university-run training in transferable skills including written and presentational skills, CV preparation etc. University-wide career coaching will be available both in Sheffield (the Think Ahead programme) and Manchester (the Researcher Development programme).
The combination of participation in research at a high level, together with the oral, written and organisational skills, as well as direct involvement with the industrial partners, will prepare outgoing members very well for future careers in industry and academia, which is of considerable benefit to the UK economy. Researchers supervised by the investigators have taken up positions in industry and academia (~50/50 split), as well as started several spin-off companies.

4. Public engagement. We will participate in various outreach activities targeting the general public, the school pupils and undergraduates in universities. Recently, we have produced a series of animations on polariton physics and quantum optics, and more recently on 2D materials, which have obtained more than 55,000 online hits. These videos were used at the Royal Society Summer Science Exhibition and the Festival of The Mind (Sheffield, 2016). Within this proposal we will create an animation describing the importance of nonlinear optics in modern technology and potential of 2D materials for such photonic applications. At Manchester, we collaborate closely with Museum of Science and Industry, where suitable exposits will be placed related to the outcomes of the proposed research.

Publications

10 25 50
 
Description We find that when two atomic layers of different transition metal dichalcogenides (MoSe2 and WS2 in our case) are attached to each other, their electronic and optical properties hybridise. This is controlled by the twist angle between the orientations of the MoSe2 and WS2 crystals. This work is published in Nature 567, 81-86 (2019).

We find a new method for preserving exciton coherence in monolayer WSe2 by placing it in an optical microcavity in the regime of the strong exciton-photon coupling. In this regime part light part matter particles are formed called polaritons which show more robust coherence properties than excitons themselves. This work is published in Nature communications 9, 4797 (2018).

We present theoretical results for the radiative rates and doping-dependent photoluminescence spectrum of interlayer excitonic complexes localized by donor impurities in MoSe2/WSe2 twisted heterobilayers, supported by quantum Monte Carlo calculations of binding energies and wave-function overlap integrals. This work is published in Physical Review B 97, 195452 (2018).
Exploitation Route So far the studies concern mostly the fundamental properties of 2D materials. However, by discovering the effect of the twist on the properties of stacked layers of 2D materials we open the way for new strategies in design of novel materials and nano-devices, which will be applied in future technologies.
Sectors Aerospace, Defence and Marine,Chemicals,Electronics,Energy,Healthcare,Manufacturing, including Industrial Biotechology

URL https://phys.org/news/2019-03-equal-graphene-like-d-materials.html
 
Title Large Area Automated Characterisation of Chemical Vapour Deposition Grown Monolayer Transition Metal Dichalcogenide Through Photoluminescence Imaging 
Description Chemical vapour deposition (CVD) growth is capable of producing multiple single crystal islands of atomically thin transition metal dichalcogenides (TMDs) over large area substrates, with potential control of their morphology, lateral size, and epitaxial alignment to substrates with hexagonal symmetry. Subsequent merging of perfectly epitaxial domains can lead to single-crystal monolayer sheets - a step towards scalable production of high quality TMDs. For CVD growth to be effectively harnessed for such production it is necessary to be able to rapidly assess the quality of material across entire large area substrates, characterising the properties of islands and allowing causality to be found with growth parameters. To date characterisation has been limited to sub 0.1 mm2 areas, where the properties measured are not necessarily representative of an entire sample. Here, we apply photoluminescence (PL) imaging and computer vision techniques to create an automated analysis for large area samples of semiconducting TMDs, measuring the properties of island size, density of islands, relative PL intensity and homogeneity, and orientation of triangular domains. The analysis is applied to 20x magnification optical microscopy images that completely map CVD samples with dimensions of up to 10 mm by 10 mm or larger. For such samples 100s of thousands objects can be identified and analysed in terms of their PL brightness and its uniformity, orientation of crystals and their size, and cross-correlation and distributions of these parameters across the entire substrate. The proposed analysis will greatly reduce the time needed to study freshly synthesised material over large area substrates and provide feedback to optimise growth conditions, advancing techniques to produce high quality TMD monolayer sheets for research and commercial applications. 
Type Of Material Improvements to research infrastructure 
Year Produced 2019 
Provided To Others? Yes  
Impact It is early days so far, but Knowledge Exchange projects funded internally by the University of Sheffield will be attempted. The basic technology has been demonstrated, and needs now to be improved to attract attention of industry. Industrial partners working on manufacturing of thin films, will be particularly targeted. 
URL https://arxiv.org/abs/1911.03633
 
Description Collaboration with the theory group of Professor Ivan Shelykh at Rekjavik University, Iceland and ITMO University, St-Petersbsurg 
Organisation ITMO University
Country Russian Federation 
Sector Academic/University 
PI Contribution Experimental studies of photons and polaritons in photonic lattices. Experimental investigation of hybrid light-matter states for quantum information processing.
Collaborator Contribution Numerical modelling of the experiment. Data analysis and interpretation. Help with the design of the experiment. Theory of collective photon states in highly nonlinear materials.
Impact Study of polaritons and photons in photonic lattices of various geometries and materials. Observation of artifical gauge field acting on photons. Study of phase modulation at room temperature Study of spin-orbit coupling. Observation of single photon phase nonlinearity. Construction of CPHASE gate with nonlinear polaritons. Joint publication in Nature Photonics paper. Other papers are under preparation
Start Year 2018
 
Description Collaboration with the theory group of Professor Ivan Shelykh at Rekjavik University, Iceland and ITMO University, St-Petersbsurg 
Organisation Reykjavík University
Country Iceland 
Sector Academic/University 
PI Contribution Experimental studies of photons and polaritons in photonic lattices. Experimental investigation of hybrid light-matter states for quantum information processing.
Collaborator Contribution Numerical modelling of the experiment. Data analysis and interpretation. Help with the design of the experiment. Theory of collective photon states in highly nonlinear materials.
Impact Study of polaritons and photons in photonic lattices of various geometries and materials. Observation of artifical gauge field acting on photons. Study of phase modulation at room temperature Study of spin-orbit coupling. Observation of single photon phase nonlinearity. Construction of CPHASE gate with nonlinear polaritons. Joint publication in Nature Photonics paper. Other papers are under preparation
Start Year 2018