arXiv subjects

Nicholas P. Sloane

Publications and source records attributed to Nicholas P. Sloane.

6 recordsLinked to original sources

arXiv2026

Multi-wavelength Spin Dynamics of Defects in Hexagonal Boron Nitride

Optically addressable solid-state spin defects are essential platforms for quantum sensing and information processing. Recently, single spin defects with combined S = 1 and S = 1/2 spin transitions were discovered in hexagonal boron nitride (hBN). In this work we unveil their excitation dynamics. In particular, we study the effects of the excitation wavelength on the spin-dependent fluorescence and the spin dynamics of these peculiar quantum spin defects. We find that changing the excitation wavelength leads to a threefold enhancement in both the optically detected magnetic resonance (ODMR) contrast and the corresponding magnetic field sensitivity. In addition, we find that the excitation wavelength has a strong impact on the photodynamics of spin complex emitters. Our work presents valuable insights to the mechanistic understanding of spin complex emitters in hBN and highlights the importance of excitation wavelength for optimising their performance in quantum sensing and quantum technologies.

cond-mat.mtrl-sci↗

arXiv2026

Spatially-resolved coherence of organic molecular spins at room-temperature

Molecular spins are a versatile platform for quantum sensing. Not only are the spin-bearing molecules themselves widely tunable, they are also capable of being used as sensors as crystals, films and in solution. Using thin-films offers the advantages of high doping ratios and the ability to control the thickness with nanometre precision, however they also introduce disorder to the system. High proximity sensing can also be realised by using micro- and nano-crystals, however in many solid-state systems this leads to a reduction in coherence. In this paper we combine room-temperature optically detected coherent control of molecular spins and microscopy to image the coherence properties of both thin-films and micro-crystals of pentacene doped p-terphenyl. In thin-films we find large amounts of variation in both the contrast and coherence times, leading to a variability in the magnetic field sensitivity of approximately 7.6 %. Applying the technique to micro-crystals shows much lower sensitivity variability (1.3 %), and we find no evidence of coherence loss toward the edge of the crystal. Finally we perform optically-detected coherent control on a nano-crystal, showing minimal loss in coherence and contrast compared to the bulk crystal, with a coherence time of 1.09 μs and a contrast of 25 %.

cond-mat.mtrl-sci↗

arXiv2025

Photodynamics and Temperature Dependence of Single Spin Defects in Hexagonal Boron Nitride

Quantum emitters in hexagonal boron nitride (hBN) that exhibit optically detected magnetic resonance (ODMR) signatures have recently garnered significant attention as an emerging solid-state platform for quantum technologies. However, the underlying spin dynamics, and the mechanisms determining the spin-dependent fluorescence in these defects are still poorly understood. In this work we perform detailed photodynamical studies of the spin complexes in hBN. In particular, we show that spin transitions are located within the metastable manifold which can be explained by the rate model, populating in a cascading manner. In addition, we perform temperature dependent measurements on these defects and show that the spin-lattice relaxation and coherence times increase as the temperature reduces. Furthermore, we find that the ODMR frequencies of the S=1 transition show only a marginal frequency shift as a function of temperature, which makes them a robust sensor at cryogenic temperatures. These insights are crucial for further understanding of the spin dynamics of quantum emitters in hBN and their practical implementation in quantum sensing.

cond-mat.mtrl-sci↗

arXiv2025

Mitigating Singlet Exciton Back-Transfer using 2D Spacer Layers for Perovskite-Sensitised Upconversion

Photon upconversion has potential applications in light-emitting diodes, photocatalysis, bio-imaging, microscopy, 3D printing, and photovoltaics. Bulk lead-halide perovskite films have emerged as promising sensitisers for solid-state photon upconversion via triplet-triplet annihilation due to their excellent optoelectronic properties. In this system, a perovskite sensitiser absorbs photons and subsequently generates triplet excitons in an adjacent emitter material, where triplet-triplet annihilation can occur allowing for the emission of higher energy photons. However, a major loss pathway in perovskite-sensitised upconversion is the back-transfer of singlet excitons from the emitter to the sensitiser via Förster Resonance Energy Transfer. In this investigation we introduce a 2D perovskite spacer layer between the bulk perovskite sensitiser and a rubrene emitter to mitigate back-transfer of singlet excitons from rubrene to the bulk perovskite sensitiser. This modification reveals the inherent balance between efficient triplet exciton transfer across the interface with a potential barrier versus the mitigation of near-field back-transfer by increasing the distance between the sensitiser and singlet excitons in the emitter. Notably, the introduction of this spacer layer enhances the relative upconversion efficiency at lower excitation power densities while also sustaining performance over extended timescales. This work represents significant progress toward the practical applications of perovskite-sensitised photon upconversion.

cond-mat.mtrl-sci↗

arXiv2025

Revealing localised dark-exciton populations in 2D perovskites via magneto-optical microscopy

The successful development of optoelectronic devices is contingent on a detailed understanding of interactions between light and excited energy states in photoactive materials. In 2D perovskites, excitons are the dominant photogenerated species and their energetic structure plays a pivotal role, governing photon absorption and emission processes. In these materials, dark exciton states can undergo photoluminescence due to the relaxation of selection rules and this process can be modulated by an external magnetic field, enabling unambiguous identification of the exciton fine structure. Previous reports of magneto-optical spectroscopy on 2D perovskites have been restricted to the macroscopic response, where key information is lost regarding the microscopic heterogeneity of the photoluminescence. Here, we use magneto-optical microscopy for the first time on perovskite materials to elucidate the spatial variation of exciton emission processes. In 2D perovskite thin films, we distinguish between regions of localised bright and dark exciton populations, correlated to the film morphology. In single crystals, we show that dark excitons become localised at the edges, where excitons can be trapped in two distinct types of sub-gap states. This work represents significant progress in understanding the properties of exciton emission in 2D perovskites, which is crucial for the development of optoelectronic technology.

cond-mat.mtrl-sci↗

arXiv2024

Electronic Structure at the Perovskite Rubrene Interface: The Effect of Surface Termination

Perovskite films have rapidly emerged as leading active materials in optoelectronic devices due to their strong optical absorption, high carrier mobility and ease of fabrication. Whilst proving to be promising materials for solar cells and light-emitting diodes, another application of perovskites which makes effective use of their unique properties is sensitisation for photon upconversion. Consisting of a bulk perovskite sensitiser alongside an adjacent organic semiconductor film, the upconverting system can absorb multiple low-energy photons to emit high-energy photons. In this work, density functional theory, in conjunction with GW theory, is utilised to investigate the electronic structure at the MAPbI$_3$/rubrene interface for different surface terminations of MAPbI$_3$. From this investigation, we reveal that the surface termination of the perovskite layer greatly affects the charge density at the interface and within the rubrene layer driven by the formation of interfacial dipole layers. The formation of a strong interfacial dipole for the lead-iodide terminated perovskite alters the band alignment of the heterojunction and is expected to facilitate more efficient hole transfer. For the perovskite surface terminated with the methylammonium iodide layer, the highest occupied molecular orbital of the adjacent rubrene layer lies deep within the perovskite band gap. This termination type is further characterized by a lower density of states near the band edges thereby acting as a spacer which is anticipated to decrease the probability of charge transfer across the interface. Thus based on our results, PbI$_2$-terminated perovskite surfaces are predicted to be favourable for applications where hole transfer to a rubrene layer is ideal, highlighting the significance of surface termination for all systems where the electronic environment at the interface is crucial to performance.

cond-mat.mtrl-sci↗