arXiv subjects

Erik C. Garnett

Publications and source records attributed to Erik C. Garnett.

9 recordsLinked to original sources

arXiv2026

Broadband Single-Particle Absorption Circular Dichroism Reveals Chiroptical Heterogeneity in Gold Helicoids

Quantitative measurements of absorption circular dichroism (CD) at the single-particle level are essential for understanding how individual chiral nanostructures dissipate optical energy, yet broadband absorptance measurements remain experimentally challenging. Here, we introduce a wavelength-tunable integrating-sphere microscope that determines the absorptance of individual nanoparticles under right- and left-circularly polarized illumination through direct optical energy balance, enabling broadband measurement of the absorption dissymmetry factor, gabs. Measurements of achiral gold nanospheres and strongly anisotropic gold nanorods establish the apparent absorption CD baseline and demonstrate minimal detectable linear-dichroism-to-circular-dichroism (LD-to-CD) leakage under the experimental conditions. Applying this approach to 87 chiral gold helicoids synthesized using L-glutathione (L-helicoids) and 96 synthesized using D-glutathione (D-helicoids) reveals mean particle-level gabs values of opposite sign, with a statistically significant difference between the two populations. Individual particles nevertheless exhibit pronounced heterogeneity in response sign, magnitude, spectral position, and line shape. More than one-third of the particles in each population display opposite-sign absorption CD responses relative to their population-average tendency. Correlative SEM analysis of the L-helicoid population further shows that opposite-sign responses persist among isolated particles exhibiting the characteristic projected helicoid morphology, indicating that aggregation and gross differences in projected morphology are insufficient to explain the observed heterogeneity. These results establish broadband single-particle absorption CD spectroscopy as a direct probe of absorptive chiroptical heterogeneity and reveal particle-specific responses obscured by ensemble averaging.

physics.optics↗

arXiv2025

Photoluminescence Mapping of Mobile and Fixed Defects in Halide Perovskite Films

Metal halide perovskites exhibit coupled electronic and ionic properties that determine their photovoltaic performance and operational stability. Understanding and quantifying ionic transport are therefore essential for advancing perovskite optoelectronics. Conventional electrical methods such as impedance spectroscopy require fully integrated devices, and their interpretation is often complicated by interfacial and contact effects, limiting the ability to isolate intrinsic ionic behavior. Here, a localized adaptation of intensity-modulated photoluminescence spectroscopy (IMPLS) is utilized to optically probe lateral ionic transport in perovskite films. The frequency-dependent photoluminescence response is measured under controlled carrier injection levels and correlated with the photoluminescence quantum yield (PLQY). The proposed diffusion model indicates that mobile ionic defects laterally migrate from high light intensity regions, giving rise to characteristic photoluminescence modulations. Ionic diffusion coefficients extracted from IMPLS agree well with literature values obtained from electrical measurements. Importantly, IMPLS mapping separates mobile and immobile defect contributions through a defect contrast coefficient (DCC), which quantifies the normalized difference between the area-averaged photoluminescence intensity and phase data. This work ultimately demonstrates that localized IMPLS provides a contact-free means to extract lateral ion diffusion coefficients while spatially distinguishing defect types across the sample.

cond-mat.mtrl-sci↗

arXiv2021

Recombination and localization: unfolding the pathways behind conductivity losses in Cs2AgBiBr6 thin films

Cs2AgBiBr6 (CABB) has been proposed as a promising non-toxic alternative to lead halide perovskites. However, low charge carrier collection efficiencies remain an obstacle for the incorporation of this material in optoelectronic applications. In this work, we study the optoelectronic properties of CABB thin films using steady state and transient absorption and reflectance spectroscopy. We find that optical measurements on such thin films are distorted as a consequence of multiple reflections within the film. Moreover, we discuss the pathways behind conductivity loss in these thin films, using a combination of microsecond transient absorption and time-resolved microwave conductivity spectroscopy. We demonstrate that a combined effect of carrier loss and localization results in the conductivity loss in CABB thin films. Moreover, we find that the charge carrier diffusion length and sample thickness are of the same order. This suggests that the materials surface is an important contributor to charge carrier loss.

cond-mat.mtrl-sci↗

arXiv2021

Intermittency of CsPbBr$_3$ perovskite quantum dots analyzed by an unbiased statistical analysis

We analyze intermittency in intensity and fluorescence lifetime of CsPbBr$_3$ perovskite quantum dots by applying unbiased Bayesian inference analysis methods. We apply changepoint analysis (CPA) and a Bayesian state clustering algorithm to determine the timing of switching events and the number of states between which switching occurs in a statistically unbiased manner, which we have benchmarked particularly to apply to highly multistate emitters. We conclude that perovskite quantum dots display a plethora of gray states in which brightness broadly speaking correlates inversely with decay rate, confirming the multiple recombination centers model. We leverage the CPA partitioning analysis to examine aging and memory effects. We find that dots tend to return to the bright state before jumping to a dim state, and that when choosing a dim state they tend to explore the entire set of states available.

cond-mat.mes-hall↗

arXiv2021

Fano lineshapes and Rabi splittings: Can they be artificially generated or obscured by the numerical aperture?

Fano resonances and Rabi splittings are routinely reported in the scientific literature. Asymmetric resonance lineshapes are usually associated with Fano resonances, and two split peaks in the spectrum are often attributed to a Rabi splitting. True Fano resonances and Rabi splittings are unequivocal signatures of coherent coupling between subsystems. However, can the same spectral lineshapes characterizing Fano resonances and Rabi splittings arise from a purely incoherent sum of intensities? Here we answer this question through experiments with a tunable Fabry-Pérot cavity containing a CsPbBr\textsubscript{3} perovskite crystal. By measuring the transmission and photoluminescence of this system using microscope objectives with different numerical aperture ($NA$), we find that even a modest $NA=0.4$ can artificially generate Fano resonances and Rabi splittings. We furthermore show that this modest $NA$ can obscure the anti-crossing of a bona fide strongly coupled light-matter system. Through transfer matrix calculations we confirm that these spectral artefacts are due to the incoherent sum of transmitted intensities at different angles captured by the $NA$. Our results are relevant to the wide nanophotonics community, characterizing dispersive optical systems with high numerical aperture microscope objectives. We conclude with general guidelines to avoid pitfalls in the characterization of such optical systems.

physics.optics↗

arXiv2019

Local Crystal Misorientation Influences Non-Radiative Recombination

We use ultrasensitive electron backscatter diffraction (EBSD) to map the local crystal orientations, grains, and grain boundaries in CH3NH3PbI3 (MAPI) perovskite thin films. Although the true grain structure is broadly consistent with the morphology visible in scanning electron microscopy (SEM), the inverse pole figure maps taken with EBSD reveal grain structure and internal misorientation that is otherwise hidden. Local crystal misorientation is consistent with the presence of local strain which varies from one grain to the next. We acquire co-aligned confocal optical photoluminescence (PL) microscopy images on the same MAPI samples used for EBSD. We correlate optical and EBSD data, showing that PL is anticorrelated with the local grain orientation spread, suggesting that grains with higher degrees of crystalline orientational heterogeneity (local strain) exhibit more non-radiative recombination. We find that larger grains tend to have larger grain orientation spread, consistent with higher degrees of strain and non-radiative recombination.

cond-mat.mtrl-sci↗

arXiv2017

Imaging a Nitrogen-Vacancy Center with a Diamond Immersion Metalens

Solid-state quantum emitters have emerged as robust single-photon sources and addressable spins: key components in rapidly developing quantum technologies for broadband magnetometry, biological sensing, and quantum information science. Performance in these applications, be it magnetometer sensitivity or quantum key generation rate, is limited by the number of photons detected. However, efficient collection of a quantum emitter's photoluminescence (PL) is challenging as its atomic scale necessitates diffraction-limited imaging with nanometer-precision alignment, oftentimes at cryogenic temperatures. In this letter, we image an individual quantum emitter, an isolated nitrogen-vacancy (NV) center in diamond, using a dielectric metalens composed of subwavelength pillars etched into the diamond's surface. The metalens eliminates the need for an objective by operating as a high-transmission-efficiency immersion lens with a numerical aperture (NA) greater than 1.0. This design provides a scalable approach for fiber coupling solid-state quantum emitters that will enable the development of deployable quantum devices.

physics.optics↗

arXiv2017

Nanoscale chiral valley-photon interface through optical spin-orbit coupling

The emergence of two-dimensional transition metal chalcogenide materials has sparked an intense activity in valleytronics since their valley information can be directly encoded and detected by using the spin angular momentum of light. For their practical applications such as on-chip valley logic gates and chip-to-chip valley transport, the encoding and processing of valley pseudospin using light should be extended to an integrated, on-chip nanophotonic system. Here, we successfully demonstrate, at room temperature, the valley-dependent directional coupling of light using a plasmonic nanowire-WS2 layers system. Our calculations show that the local transverse spin angular momentum of the mode of the plasmonic nanowire provides robust optical spin-path locking of up to 91 %. Experimentally we demonstrate that valley pseudospin in WS2 is coupled with optical spin of the same handedness and exhibits a high directional coupling efficiency up to 90 % to the plasmonic guided mode. The result opens up new avenues of controlling, detecting and processing valley and spin information with precise optical control at the nanoscale.

physics.optics↗

arXiv2016

Indirect to direct bandgap transition in methylammonium lead halide perovskite

Methylammonium lead iodide perovskites are considered direct bandgap semiconductors. Here we show that in fact they present a weakly indirect bandgap 60 meV below the direct bandgap transition. This is a consequence of spin-orbit coupling resulting in Rashba-splitting of the conduction band. The indirect nature of the bandgap explains the apparent contradiction of strong absorption and long charge carrier lifetime. Under hydrostatic pressure from ambient to 325 MPa, Rashba splitting is reduced due to a pressure induced ordering of the crystal structure. The nature of the bandgap becomes increasingly more direct, resulting in five times faster charge carrier recombination, and a doubling of the radiative efficiency. At hydrostatic pressures above 325 MPa, MAPI undergoes a reversible phase transition resulting in a purely direct bandgap semiconductor. The pressure-induced changes suggest epitaxial and synthetic routes to higher efficiency optoelectronic devices.

cond-mat.mtrl-sci↗