Periodic Reporting for period 4 - LIMA (Controlling light-matter interactions by quantum designed 2D materials)
Berichtszeitraum: 2022-10-01 bis 2023-09-30
The overarching idea of LIMA is to use advanced quantum mechanical computer simulations to perform rational design of new materials with tailored optical properties that can be used for high-efficiency solar cells and single- photon quantum technologies, respectively. In terms of materials, the focus is primarily, but not exclusively, on atomically thin two-dimensional (2D) materials, which represent an emergent class of materials with quite distinct properties as compared to conventional bulky materials. One important specific aim is the identification of novel layered structures composed of 2D materials stacked in a carefully designed sequence with potential to reach solar-to-electricity power conversion efficiencies in excess of 50%. Another specific goal is to find stable point defects in wide band gap insulators that can be used to realize “on demand” single photon light sources - a fundamental prerequisite for several emergent quantum technologies including quantum communication. To reach these goals, the project will develop computational methods for quantifying the non-radiative losses that limit light-matter interactions, and thereby enable a realistic assessment of the actual performance of a given material. With its rational approach to materials design, LIMA will help to accelerate the development of new and improved optical materials to the benefit of our economy and society.
The LIMA project has resulted in several scientific discoveries. Some of the most important include: The theoretical prediction and experimental demonstration of electrically tunable, optically active interlayer excitons in bilayer MoS2. The significant expansion of the Computational 2D Materials Database by 4000 stable monolayers. The construction of a new database of van der Waals homobilayers with a variety of calculated properties. The detailed characterisation of the properties of point defects responsible for single-photon emission around 2 eV in hexagonal boron nitride. The creation of a computational database (the QPOD database) of point defects in 2D materials. The introduction of a new type of 2D materials produced by self-intercalation in the van der Waals gap of a homobilayer and a high-throughput characterisation of the basic properties of many such structures.
The LIMA project has resulted in several scientific discoveries. Some of the most important include: The theoretical prediction and experimental demonstration of electrically tunable, optically active interlayer excitons in bilayer MoS2. The significant expansion of the Computational 2D Materials Database by 4000 stable monolayers. The construction of a new database of van der Waals homobilayers with a variety of calculated properties. The detailed characterisation of the properties of point defects responsible for single-photon emission around 2 eV in hexagonal boron nitride. The creation of a computational database (the QPOD database) of point defects in 2D materials. The introduction of a new type of 2D materials produced by self-intercalation in the van der Waals gap of a homobilayer and a high-throughput characterisation of the basic properties of many such structures.
An important milestone in the initial phase of LIMA was the launching of the Computational 2D Materials Database (C2DB) – a fully open and searchable online database containing structures and a variety of electronic, optical and magnetic properties for monolayer 2D materials (https://cmr.fysik.dtu.dk/c2db/c2db.html(öffnet in neuem Fenster)). The first version of C2DB contained about 4000 materials. During the LIMA project, the C2DB has formed the basis for high-throughput screening studies where a number of novel 2D materials were identified and studied. In particular, we have discovered 2D ferromagnetic and ferroelectric semiconductors as well as topological insulators. The results of these screening studies have been published in Physical Review M, npj Computational Materials, and 2D Materials. A new type of 2D materials with broken mirror symmetries – the so-called Janus monolayers – have been investigated thoroughly, and their potential as building blocks for advanced opto-electronic devices has been demonstrated and disseminated in several papers. During the course of the project period the C2DB has been significantly expanded both in terms of new materials and new properties. Using a combination of systematic atom substitution and a deep generative machine learning model, we have identified around 10k new 2D crystals. The basic properties of the 4500 most stable of these crystals have been characterized using first principles calculations and have been made available in the C2DB.
Two comprehensive papers on the C2DB were published in 2D Materials and are among the highest cited papers of the journal.
We have studied a range of properties of excitons (bound electron-hole pairs) in 2D semiconductors; mainly monolayer and bilayer transition metal dichalcogenides (TMDs). In particular, we have performed the first predictions of interlayer trions in 2D heterobilayers. These theoretical predictions were subsequently observed experimentally and good agreement was found with our calculated binding energies. We have calculated the full q-dispersion of the lowest lying excitons in monolayer and homobilayer TMDs and also the properties of the dark excitons in these materials. We introduced and studied the important concept of mixed interlayer excitons in bilayer TMDs. These excitons have a mixed intralayer and interlayer character. In a subsequent collaboration with Prof. Saverio Russo at Exeter University we demonstrated electrical tuning of mixed interlayer excitons in bilayer MoS2. This work was published in Nature Nanotechnology.
A large number of 2D point defects for quantum technology applications (single-photon light sources and qbits) been explored. In particular, the photo-physics of native and carbon-containing defects in hexagonal boron-nitride (hBN) has been studied in detail in collaboration with experimental groups at the Technical University of Denmark. The results of these studies have been published in Nanoscale and 2D Materials. Using high-throughput computations we have systematically calculated the properties of around 1800 native point defects in 80 different 2D materials. The results have been compiled and curated and made available to the scientific community via the QPOD database, which is freely available online. A paper on QPOD was published in npj Computational Materials. Like the BiDB bilayer database, the QPOD database is integrated with the C2DB.
To discover point defects with a triplet ground state and narrow emission lineshapes, we conducted a high-throughput computational screening of 5000 point defects in ten 2D host materials. The defects comprised both native and extrinsic single and double defects. We were able to identify a short list of 20 point defects with very promising properties making them interesting candidates for quantum applications. The results were published in ACS Nano and will be made available via QPOD.
Two comprehensive papers on the C2DB were published in 2D Materials and are among the highest cited papers of the journal.
We have studied a range of properties of excitons (bound electron-hole pairs) in 2D semiconductors; mainly monolayer and bilayer transition metal dichalcogenides (TMDs). In particular, we have performed the first predictions of interlayer trions in 2D heterobilayers. These theoretical predictions were subsequently observed experimentally and good agreement was found with our calculated binding energies. We have calculated the full q-dispersion of the lowest lying excitons in monolayer and homobilayer TMDs and also the properties of the dark excitons in these materials. We introduced and studied the important concept of mixed interlayer excitons in bilayer TMDs. These excitons have a mixed intralayer and interlayer character. In a subsequent collaboration with Prof. Saverio Russo at Exeter University we demonstrated electrical tuning of mixed interlayer excitons in bilayer MoS2. This work was published in Nature Nanotechnology.
A large number of 2D point defects for quantum technology applications (single-photon light sources and qbits) been explored. In particular, the photo-physics of native and carbon-containing defects in hexagonal boron-nitride (hBN) has been studied in detail in collaboration with experimental groups at the Technical University of Denmark. The results of these studies have been published in Nanoscale and 2D Materials. Using high-throughput computations we have systematically calculated the properties of around 1800 native point defects in 80 different 2D materials. The results have been compiled and curated and made available to the scientific community via the QPOD database, which is freely available online. A paper on QPOD was published in npj Computational Materials. Like the BiDB bilayer database, the QPOD database is integrated with the C2DB.
To discover point defects with a triplet ground state and narrow emission lineshapes, we conducted a high-throughput computational screening of 5000 point defects in ten 2D host materials. The defects comprised both native and extrinsic single and double defects. We were able to identify a short list of 20 point defects with very promising properties making them interesting candidates for quantum applications. The results were published in ACS Nano and will be made available via QPOD.
The C2DB computational database launched by LIMA in 2018 is by far the largest and most comprehensive of its kind (in terms of calculated and stored properties) and represents a significant step beyond the state of the art. The same holds for the BiDB and QPOD databases. Together the three databases (C2DB, BiDB, and QPOD) form a unique digital platform that will continue to support and accelerate 2D materials science in the future. These databases and results produced on the basis of them has been published in numerous papers. The work on intersubband transitions in ultrathin van der Waals materials (Nature Nanotechnology 2018) represents a completely new concept with an interesting potential for optical devices in the mid-infrared frequency regime. Similarly, the mixed interlayer excitons in bilayer 2D materials that were first introduced by us (Nano Letters from 2018) and subsequently demonstrated experimentally (Nature Nanotechnology 2021), represents an important breakthrough enabling electrically tunable light manipulation in 2D materials. Similarly, the work on self-intercalated 2D materials (Nature 2020) introduced a new class of crystalline 2D materials whose properties can be tuned by varying the concentration of intercalated atoms.