Current projects and laboratories
Here we describe our current projects (as of October 2022) and our experimental capabilities.
Sub-wavelength all-dielectric nano-photonics
So far nano-photonics has dealt with dielectric devices relying on confining light in diffraction-limited volumes. Beating the diffraction limit by confining light on sub-wavelength scales has been only possible with plasmonic structures made of nano-structured metal, which unavoidably suffer from large optical losses.
Recently, it has been shown that high-refractive-index dielectric nano-antennas can provide confined optical modes with sub-wavelength mode volumes. In contrast to plasmonic devices, such structures show negligible non-radiative losses.
Our research group has shown that by coupling such antennas to atomically thin 2D semiconductors - transition metal dichalcogenides (TMDs), strong fluorescence enhancements in the latter can be observed. See our paper on this topic in Nature Communications.
In this project we are expanding the nano-photonics ‘tool-box’ by studying unexplored materials systems and realising innovative approaches for a new generation of dielectric nano-antennas and nano-photonic structures and their coupling to various fluorescent materials.
Our recent papers on this topic have been published in ACS Nano and on arxiv.
Optical manifestations of the quantum physics of moiré superlattices in van der Waals heterostructures
Atomically-thin layers of two-dimensional materials can be assembled in vertical stacks (called ‘heterostructures’), which are held together by relatively weak van der Waals forces, allowing for coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation, or ‘twist’.
The twist is a new degree of freedom recently discovered in 2D materials and now widely used in the design of 2D heterostructures. It leads to a new in-plane periodicity in the local atomic registry of the constituent crystal structures, known as a moiré superlattice.
The moiré superlattice has a dramatic effect on the motion of electrons in the plane of the 2D structure. For example, when two monolayers of graphene are attached to each other with a ‘magic twist angle’ a superconductor-insulator transition is observed.
Similarly, in 2D semiconductors, the twist has been shown to lead to a variety of unusual optical phenomena as we reported in our recent work in Nature. In this project, we will explore this new degree of freedom in a variety of layered materials and new phenomena and physics will be discovered.
Strong light-matter interaction in van der Waals 2D materials
Here we focus on studies of the strong light-matter interaction in 2D materials embedded in optical microcavities and coupled to various photonic structures.
New states of the matter, exciton-polaritons emerge in these structures, which provide a particularly rich phenomenology in atomically thin transition metal dichalcogenides (TMDs), as we have shown in our recent papers in:
Further unexplored strong-coupling phenomena, for example in high density electron gas in the extreme 2D limit will be studied in this project opening unprecedented possibilities to explore new non-linear optical phenomena and device applications.
Nano-magnetism in atomically thin 2D quantum materials and their heterostructures
In a large family of layered crystals the properties range from superconductors and metals, to semiconductors and insulators. Properties of such quantum materials in a few-atomic-layer form are strongly influenced by the quantum confinement of the electronic excitations due to the extreme crystal thinness.
Surprisingly, a family of layered ferromagnetic materials exists, which preserve their ferromagnetic properties even in an atomic monolayer form. Such 2D materials will revolutionise electronics, memory devices, and will have broad applications in quantum technologies, particularly in combination with other layered semiconductors.
In this PhD project we will discover novel magnetic few-atomic-layer materials, work on advancing their fabrication, and develop methods for combining such materials with other 2D monolayer crystals such as transition metal dichalcogenides (TMDs).
The goal is to fabricate and explore novel types of opto-electronic devices taking advantage of various magnetic proximity effects generated by 2D magnetic materials on the nano-scale, as shown in our work in Nature Communications.
Our expertise is in photonics and magneto-optics of nano-structured semiconductors. The group occupies three dedicated high-spec optical laboratories (including a state-of-the-art vector-magnet magneto-optics and Raman set-up) and shares access to several other state-of-the-art optics laboratories in the LDSD group. We have established a 2D materials fabrication facility including a glovebox that ensures high quality heterostructure assembly as well as allows working with air-sensitive 2D materials. Finally, we have launched a new Near-field Optical Imaging and Spectroscopy Centre (NOSC), where we have access to a range of tip-enhanced optical techniques and nano-spectroscopy.
Several of our set-ups are quite unique, even among the world leading optics groups. For example, we have a tunable Fabri-Perot microcavity set-up installed in a vector magnetic field cryostat where 4.5T can be rotated in 2D plane. This cryostat also has 9T maximum vertical magnetic field. The NOSC lab has a unique combination of excitation lasers and detectors in a wide range of wavelength including visible, near-infrared and mid-infrared.
Microscopes in one of the labs used for sample fabrication and for characterisation of nano-photonic devices in ambient conditions.
Set-up for cryogenic ultra-low frequency Raman spectroscopy uniquely designed for studies of magnetic and superconducting layered and atomically thin materials. Oscar Hutchings is aligning the set-up. Autumn 2020.
A typical micro-photoluminescence and micro-reflectance set-up for spectroscopy from cryogenic to room temperature, a work-horse of our experiments replicated in several labs.
Flake transfer set-up in a nitrogen-purged glovebox. The set-up will be equipped with optical characterisation allowing to measure air-sensitive materials and structures as soon as they've been made. July 2022.