Direct visualization of relativistic quantum scars in graphene quantum dots.

Quantum scars refer to eigenstates with enhanced probability density along unstable classical periodic orbits. First predicted 40 years ago, scars are special eigenstates that counterintuitively defy ergodicity in quantum systems whose classical counterpart is chaotic. Despite the importance and long history of scars, their direct visualization in quantum systems remains an open field.

Structure, morphology and surface properties of α-lactose monohydrate in relation to its powder properties.

The particulate properties of α-lactose monohydrate (αLMH), an excipient and carrier for pharmaceuticals, is important for the design, formulation and performance of a wide range of drug products. Here an integrated multi-scale workflow provides a detailed molecular and inter-molecular (synthonic) analysis of its crystal morphology, surface chemistry and surface energy. Predicted morphologies are validated in 3D through X-ray diffraction (XCT) contrast tomography.

Valley-Hybridized Gate-Tunable 1D Exciton Confinement in MoSe.

Controlling excitons at the nanoscale in semiconductor materials represents a formidable challenge in the quantum photonics and optoelectronics fields. Monolayers of transition metal dichalcogenides (TMDs) offer inherent 2D confinement and possess significant exciton binding energies, making them promising candidates for achieving electric-field-based confinement of excitons without dissociation. Exploiting the valley degree of freedom associated with these confined states further broadens the prospects for exciton engineering.

Ultimate Charge Transport Regimes in Doping-Controlled Graphene Laminates: Phonon-Assisted Processes Revealed by the Linear Magnetoresistance.

Understanding and controlling the electrical properties of solution-processed 2D materials is key to further printed electronics progress. Here, we demonstrate that the thermolysis of the aromatic intercalants utilized in nanosheet exfoliation for graphene laminates allows for high intrinsic mobility and the simultaneous control of doping type (- and -) and concentration over a wide range. We establish that the intraflake mobility is high by observing a linear magnetoresistance of such solution-processed graphene laminates and using it to devolve the interflake tunneling and intralayer magnetotransport.

Localized thermal emission from topological interfaces.

The control of thermal radiation by shaping its spatial and spectral emission characteristics plays a key role in many areas of science and engineering. Conventional approaches to tailoring thermal emission using metamaterials are hampered both by the limited spatial resolution of the required subwavelength material structures and by the materials' strong absorption in the infrared. In this work, we demonstrate an approach based on the concept of topology.

Tunnel junctions based on interfacial two dimensional ferroelectrics.

Van der Waals heterostructures have opened new opportunities to develop atomically thin (opto)electronic devices with a wide range of functionalities. The recent focus on manipulating the interlayer twist angle has led to the observation of out-of-plane room temperature ferroelectricity in twisted rhombohedral bilayers of transition metal dichalcogenides. Here we explore the switching behaviour of sliding ferroelectricity using scanning probe microscopy domain mapping and tunnelling transport measurements.

A Wrist-Worn Internet of Things Sensor Node for Wearable Equivalent Daylight Illuminance Monitoring.

Light exposure is a vital regulator of physiology and behavior in humans. However, monitoring of light exposure is not included in current wearable Internet of Things (IoT) devices, and only recently have international standards defined [Formula: see text] -optic equivalent daylight illuminance (EDI) measures for how the eye responds to light. This article reports a wearable light sensor node that can be incorporated into the IoT to provide monitoring of EDI exposure in real-world settings.

One-dimensional proximity superconductivity in the quantum Hall regime.

Extensive efforts have been undertaken to combine superconductivity and the quantum Hall effect so that Cooper-pair transport between superconducting electrodes in Josephson junctions is mediated by one-dimensional edge states. This interest has been motivated by prospects of finding new physics, including topologically protected quasiparticles, but also extends into metrology and device applications. So far it has proven challenging to achieve detectable supercurrents through quantum Hall conductors.

Competition of Moiré Network Sites to Form Electronic Quantum Dots in Reconstructed MoX/WX Heterostructures.

Twisted bilayers of two-dimensional semiconductors offer a versatile platform for engineering quantum states for charge carriers using moiré superlattice effects. Among the systems of recent interest are twistronic MoX/WX heterostructures (X = Se or S), which undergo reconstruction into preferential stacking domains and highly strained domain wall networks, determining the electron/hole localization across moiré superlattices. Here, we present a catalogue of options for the formation of self-organized quantum dots and wires in lattice-reconstructed marginally twisted MoX/WX bilayers with a relative lattice mismatch δ ≪ 1 for twist angles ranging from perfect alignment to θ ∼ 1°.

Resonant Band Hybridization in Alloyed Transition Metal Dichalcogenide Heterobilayers.

Bandstructure engineering using alloying is widely utilized for achieving optimized performance in modern semiconductor devices. While alloying has been studied in monolayer transition metal dichalcogenides, its application in van der Waals heterostructures built from atomically thin layers is largely unexplored. Here, heterobilayers made from monolayers of WSe (or MoSe) and MoWSe alloy are fabricated and nontrivial tuning of the resultant bandstructure is observed as a function of concentration x.

Kagome Quantum Oscillations in Graphene Superlattices.

Electronic spectra of solids subjected to a magnetic field are often discussed in terms of Landau levels and Hofstadter-butterfly-style Brown-Zak minibands manifested by magneto-oscillations in two-dimensional electron systems. Here, we present the semiclassical precursors of these quantum magneto-oscillations which appear in graphene superlattices at low magnetic field near the Lifshitz transitions and persist at elevated temperatures. These oscillations originate from Aharonov-Bohm interference of electron waves following open trajectories that belong to a kagome-shaped network of paths characteristic for Lifshitz transitions in the moire superlattice minibands of twistronic graphenes.

Twirling and Spontaneous Symmetry Breaking of Domain Wall Networks in Lattice-Reconstructed Heterostructures of Two-Dimensional Materials.

Lattice relaxation in twistronic bilayers with close lattice parameters and almost perfect crystallographic alignment of the layers results in the transformation of the moiré pattern into a sequence of preferential stacking domains and domain wall networks. Here, we show that reconstructed moiré superlattices of the perfectly aligned heterobilayers of same chalcogen transition metal dichalcogenides have broken-symmetry structures featuring twisted nodes ("twirls") of domain wall networks. The analysis of twist-angle dependence of strain characteristics for the broken-symmetry structures shows that the formation of twirl reduces the amount of hydrostatic strain around the nodes, potentially weakening their influence on the band edge energies of electrons and holes.

Microstructural insight into inhalation powder blends through correlative multi-scale X-ray computed tomography.

Dry powder inhalers (DPI) are important for topical drug delivery to the lungs, but characterising the pre-aerosolised powder microstructure is a key initial step in understanding the post-aerosolised blend performance. In this work, we characterise the pre-aerosolised 3D microstructure of an inhalation blend using correlative multi-scale X-ray Computed Tomography (XCT), identifying lactose and drug-rich phases at multiple length scales on the same sample. The drug-rich phase distribution across the sample is shown to be homogeneous on a bulk scale but heterogeneous on a particulate scale, with individual clusters containing different amounts of drug-rich phase, and different parts of a carrier particle coated with different amounts of drug-rich phase.

Mixing of moiré-surface and bulk states in graphite.

Van der Waals assembly enables the design of electronic states in two-dimensional (2D) materials, often by superimposing a long-wavelength periodic potential on a crystal lattice using moiré superlattices. This twistronics approach has resulted in numerous previously undescribed physics, including strong correlations and superconductivity in twisted bilayer graphene, resonant excitons, charge ordering and Wigner crystallization in transition-metal chalcogenide moiré structures and Hofstadter's butterfly spectra and Brown-Zak quantum oscillations in graphene superlattices. Moreover, twistronics has been used to modify near-surface states at the interface between van der Waals crystals.

Electrochemical assessment of a tripodal thiourea-based anion receptor at the liquid|liquid interface.

Thiourea-based receptors for anions have been widely studied due to their ability to transport anions across phospholipid bilayers. The binding affinity of a tripodal thiourea-based receptor for anions was assessed at the aqueous|organic interface using electrochemical measurements. A 1 : 1 stoichiometry was determined for the complexation of most anions, with a higher stoichiometry found in the presence of excess Cl and Br anions.

Ferroelectric Switching at Symmetry-Broken Interfaces by Local Control of Dislocations Networks.

Semiconducting ferroelectric materials with low energy polarization switching offer a platform for next-generation electronics such as ferroelectric field-effect transistors. Recently discovered interfacial ferroelectricity in bilayers of transition metal dichalcogenide films provides an opportunity to combine the potential of semiconducting ferroelectrics with the design flexibility of 2D material devices. Here, local control of ferroelectric domains in a marginally twisted WS bilayer is demonstrated with a scanning tunneling microscope at room temperature, and their observed reversible evolution is understood using a string-like model of the domain wall network (DWN).

Optimization of thermoelectric properties of carbon nanotube veils by defect engineering.

Carbon nanotubes (CNTs), with their combination of excellent electrical conductivity, Seebeck coefficient, mechanical robustness and environmental stability are highly desired as thermoelectric (TE) materials for a wide range of fields including Internet of Things, health monitoring and environmental remediation solutions. However, their high thermal conductivity () is an obstacle to practical TE applications. Herein, we present a novel method to reduce the of CNT veils, by introducing defects, while preserving their Seebeck coefficient and electrical conductivity.

Reversible Ionic Liquid Intercalation for Electrically Controlled Thermal Radiation from Graphene Devices.

Using graphene as a tunable optical material enables a series of optical devices such as switchable radar absorbers, variable infrared emissivity surfaces, or visible electrochromic devices. These devices rely on controlling the charge density on graphene with electrostatic gating or intercalation. In this paper, we studied the effect of ionic liquid intercalation on the long-term performance of optoelectronic devices operating within a broad infrared wavelength range.

Mixed-Stacking Few-Layer Graphene as an Elemental Weak Ferroelectric Material.

Ferroelectricity (Valasek, J. 1921, 17, 475), a spontaneous formation of electric polarization, is a solid state phenomenon, usually, associated with ionic compounds or complex materials. Here we show that, atypically for elemental solids, few-layer graphenes can host an equilibrium out-of-plane electric polarization, switchable by sliding the constituent graphene sheets.

Giant orbital magnetic moments and paramagnetic shift in artificial relativistic atoms and molecules.

Materials such as graphene and topological insulators host massless Dirac fermions that enable the study of relativistic quantum phenomena. Single quantum dots and coupled quantum dots formed with massless Dirac fermions can be viewed as artificial relativistic atoms and molecules, respectively. Such structures offer a unique testbed to study atomic and molecular physics in the ultrarelativistic regime (particle speed close to the speed of light).

Moiré modulation of charge density waves.

Here we investigate how charge density waves (CDWs), inherent to a monolayer, are effected by creating twisted van der Waals structures. Homobilayers of metallic transition metal dichalcogenides (TMDs), at small twist angles where there is significant atomic reconstruction, are utilised as an example to investigate the interplay between the moiré domain structure and CDWs of different periods. For3×3CDWs, there is no geometric constraint to prevent the CDWs from propagating throughout the moiré structure.

Band Gap Opening in Bilayer Graphene-CrCl/CrBr/CrI van der Waals Interfaces.

We report experimental investigations of transport through bilayer graphene (BLG)/chromium trihalide (CrX; X = Cl, Br, I) van der Waals interfaces. In all cases, a large charge transfer from BLG to CrX takes place (reaching densities in excess of 10 cm), and generates an electric field perpendicular to the interface that opens a band gap in BLG. We determine the gap from the activation energy of the conductivity and find excellent agreement with the latest theory accounting for the contribution of the σ bands to the BLG dielectric susceptibility.

Light sources with bias tunable spectrum based on van der Waals interface transistors.

Light-emitting electronic devices are ubiquitous in key areas of current technology, such as data communications, solid-state lighting, displays, and optical interconnects. Controlling the spectrum of the emitted light electrically, by simply acting on the device bias conditions, is an important goal with potential technological repercussions. However, identifying a material platform enabling broad electrical tuning of the spectrum of electroluminescent devices remains challenging.

Strong Coupling of Carbon Quantum Dots in Liquid Crystals.

Carbon quantum dots (CDs) have recently received a tremendous amount of interest owing to their attractive optical properties. However, CDs have broad absorption and emission spectra limiting their application ranges. We herein, for the first time, show synthesis of water-soluble red emissive CDs with a very narrow line width (∼75 meV) spectral absorbance and hence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystalline mesophases.

Topological engineering of terahertz light using electrically tunable exceptional point singularities.

The topological structure associated with the branch point singularity around an exceptional point (EP) can provide tools for controlling the propagation of light. Through use of graphene-based devices, we demonstrate the emergence of EPs in an electrically controlled interaction between light and a collection of organic molecules in the terahertz regime at room temperature. We show that the intensity and phase of terahertz pulses can be controlled by a gate voltage, which drives the device across the EP.