Fundamental limits to graphene plasmonics.

Plasmon polaritons are hybrid excitations of light and mobile electrons that can confine the energy of long-wavelength radiation at the nanoscale. Plasmon polaritons may enable many enigmatic quantum effects, including lasing 1 , topological protection2,3 and dipole-forbidden absorption 4 . A necessary condition for realizing such phenomena is a long plasmonic lifetime, which is notoriously difficult to achieve for highly confined modes 5 . Plasmon polaritons in graphene-hybrids of Dirac quasiparticles and infrared photons-provide a platform for exploring light-matter interaction at the nanoscale6,7. However, plasmonic dissipation in graphene is substantial 8 and its fundamental limits remain undetermined. Here we use nanometre-scale infrared imaging to investigate propagating plasmon polaritons in high-mobility encapsulated graphene at cryogenic temperatures. In this regime, the propagation of plasmon polaritons is primarily restricted by the dielectric losses of the encapsulated layers, with a minor contribution from electron-phonon interactions. At liquid-nitrogen temperatures, the intrinsic plasmonic propagation length can exceed 10 micrometres, or 50 plasmonic wavelengths, thus setting a record for highly confined and tunable polariton modes. Our nanoscale imaging results reveal the physics of plasmonic dissipation and will be instrumental in mitigating such losses in heterostructure engineering applications.

A core outcome set for hyperemesis gravidarum research: an international consensus study.

OBJECTIVE: To develop a core outcome set for trials on the treatment of hyperemesis gravidarum (HG). DESIGN: Identification of outcomes is followed by a modified Delphi survey combined with a consensus development meeting and a consultation round. SETTING: An international web-based survey combined with a consensus development meeting. POPULATION: Stakeholders including researchers; women with lived experience of HG and their families; obstetric health professionals; and other health professionals. METHODS: We used systematic review, semi-structured patient interviews, closed group sessions and Steering Committee input to identify potential core outcomes. We conducted two web-based survey rounds, followed by a face-to-face consensus development meeting and a web-based consultation round. MAIN OUTCOME MEASURES: A core outcome set for research on HG. RESULTS: Fifty-six potential outcomes were identified. The modified Delphi process was completed by 125 stakeholders, the consensus development meeting by 20 stakeholders and the consultation round by 96 stakeholders. Consensus was reached in ten domains on 24 outcomes: nausea; vomiting; inability to tolerate oral fluids or food; dehydration; weight difference; electrolyte imbalance; intravenous fluid treatment; use of medication for hyperemesis gravidarum; hospital treatment; treatment compliance; patient satisfaction; daily functioning; maternal physical or mental or emotional wellbeing; short- and long-term adverse effects of treatment; maternal death; pregnancy complications; considering or actually terminating a wanted pregnancy; preterm birth; small for gestational age; congenital anomalies; neonatal morbidity and offspring death). CONCLUSIONS: This core outcome set will help standardise outcome reporting in HG trials. TWEETABLE ABSTRACT: A core outcome set for treatment of hyperemesis gravidarum in order to create high-quality evidence.

Defects in Efflux (oprM), ß-Lactamase (ampC), and Lipopolysaccharide Transport (lptE) Genes Mediate Antibiotic Hypersusceptibility of Pseudomonas aeruginosa Strain Z61.

Antibiotic hypersensitive bacterial mutants (e.g., Escherichia coliimp) are used to investigate intrinsic resistance and are exploited in antibacterial discovery to track weak antibacterial activity of novel inhibitor compounds. Pseudomonas aeruginosa Z61 is one such drug-hypersusceptible strain generated by chemical mutagenesis, although the genetic basis for hypersusceptibility is not fully understood. Genome sequencing of Z61 revealed nonsynonymous single-nucleotide polymorphisms in 153 genes relative to its parent strain, and three candidate mutations (in oprM, ampC, and lptE) predicted to mediate hypersusceptibility were characterized. The contribution of these mutations was confirmed by genomic restoration of the wild-type sequences, individually or in combination, in the Z61 background. Introduction of the lptE mutation or genetic inactivation of oprM and ampC genes alone or together in the parent strain recapitulated drug sensitivities. This showed that disruption of oprM (which encodes a major outer membrane efflux pump channel) increased susceptibility to pump substrate antibiotics, that inactivation of the inducible ß-lactamase gene ampC contributed to ß-lactam susceptibility, and that mutation of the lipopolysaccharide transporter gene lptE strongly altered the outer membrane permeability barrier, causing susceptibility to large antibiotics such as rifampin and also to ß-lactams.

High-Quality Magnetotransport in Graphene Using the Edge-Free Corbino Geometry.

We report fabrication of graphene devices in a Corbino geometry consisting of concentric circular electrodes with no physical edge connecting the inner and outer electrodes. High device mobility is realized using boron nitride encapsulation together with a dual-graphite gate structure. Bulk conductance measurement in the quantum Hall effect (QHE) regime outperforms previously reported Hall bar measurements, with improved resolution observed for both the integer and fractional QHE states. We identify apparent phase transitions in the fractional sequence in both the lowest and first excited Landau levels (LLs) and observe features consistent with electron solid phases in higher LLs.

Hofstadter's butterfly and the fractal quantum Hall effect in moiré superlattices.

Electrons moving through a spatially periodic lattice potential develop a quantized energy spectrum consisting of discrete Bloch bands. In two dimensions, electrons moving through a magnetic field also develop a quantized energy spectrum, consisting of highly degenerate Landau energy levels. When subject to both a magnetic field and a periodic electrostatic potential, two-dimensional systems of electrons exhibit a self-similar recursive energy spectrum. Known as Hofstadter's butterfly, this complex spectrum results from an interplay between the characteristic lengths associated with the two quantizing fields, and is one of the first quantum fractals discovered in physics. In the decades since its prediction, experimental attempts to study this effect have been limited by difficulties in reconciling the two length scales. Typical atomic lattices (with periodicities of less than one nanometre) require unfeasibly large magnetic fields to reach the commensurability condition, and in artificially engineered structures (with periodicities greater than about 100 nanometres) the corresponding fields are too small to overcome disorder completely. Here we demonstrate that moiré superlattices arising in bilayer graphene coupled to hexagonal boron nitride provide a periodic modulation with ideal length scales of the order of ten nanometres, enabling unprecedented experimental access to the fractal spectrum. We confirm that quantum Hall features associated with the fractal gaps are described by two integer topological quantum numbers, and report evidence of their recursive structure. Observation of a Hofstadter spectrum in bilayer graphene means that it is possible to investigate emergent behaviour within a fractal energy landscape in a system with tunable internal degrees of freedom.

Negative Coulomb Drag in Double Bilayer Graphene.

We report on an experimental measurement of Coulomb drag in a double quantum well structure consisting of bilayer-bilayer graphene, separated by few layer hexagonal boron nitride. At low temperatures and intermediate densities, a novel negative drag response with an inverse sign is observed, distinct from the momentum and energy drag mechanisms previously reported in double monolayer graphene. By varying the device aspect ratio, the negative drag component is suppressed and a response consistent with pure momentum drag is recovered. In the momentum drag dominated regime, excellent quantitative agreement with the density and temperature dependence predicted for double bilayer graphene is found.

Visualizing moiré ferroelectricity via plasmons and nano-photocurrent in graphene/twisted-WSe2 structures.

Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) materials. The discovery of ferroelectricity in twisted vdW layers provides new opportunities to engineer spatially dependent electric and optical properties associated with the configuration of moiré superlattice domains and the network of domain walls. Here, we employ near-field infrared nano-imaging and nano-photocurrent measurements to study ferroelectricity in minimally twisted WSe2. The ferroelectric domains are visualized through the imaging of the plasmonic response in a graphene monolayer adjacent to the moiré WSe2 bilayers. Specifically, we find that the ferroelectric polarization in moiré domains is imprinted on the plasmonic response of the graphene. Complementary nano-photocurrent measurements demonstrate that the optoelectronic properties of graphene are also modulated by the proximal ferroelectric domains. Our approach represents an alternative strategy for studying moiré ferroelectricity at native length scales and opens promising prospects for (opto)electronic devices.

Nano-spectroscopy of excitons in atomically thin transition metal dichalcogenides.

Excitons play a dominant role in the optoelectronic properties of atomically thin van der Waals (vdW) semiconductors. These excitons are amenable to on-demand engineering with diverse control knobs, including dielectric screening, interlayer hybridization, and moiré potentials. However, external stimuli frequently yield heterogeneous excitonic responses at the nano- and meso-scales, making their spatial characterization with conventional diffraction-limited optics a formidable task. Here, we use a scattering-type scanning near-field optical microscope (s-SNOM) to acquire exciton spectra in atomically thin transition metal dichalcogenide microcrystals with previously unattainable 20 nm resolution. Our nano-optical data revealed material- and stacking-dependent exciton spectra of MoSe2, WSe2, and their heterostructures. Furthermore, we extracted the complex dielectric function of these prototypical vdW semiconductors. s-SNOM hyperspectral images uncovered how the dielectric screening modifies excitons at length scales as short as few nanometers. This work paves the way towards understanding and manipulation of excitons in atomically thin layers at the nanoscale.

The windsor definition for hyperemesis gravidarum: A multistakeholder international consensus definition.

OBJECTIVE: To develop an international definition for hyperemesis gravidarum to assist in clinical diagnosis and harmonize hyperemesis gravidarum definition for study populations. STUDY DESIGN: A mixed-methods approach was used to identify potential hyperemesis gravidarum definition criteria (i.e. systematic review, semi-structured interviews and closed group sessions with patients and Project Steering Committee input). To reach consensus on the definition we used a web-based Delphi survey with two rounds, followed by a face-to-face consensus development meeting, held in Windsor UK, and a web-based consultation round, in which the provisional hyperemesis gravidarum definition was fed back to the stakeholders. Four stakeholder groups were identified 1) researchers; 2) women with lived experience of hyperemesis gravidarum and their families; 3) obstetric health professionals (obstetricians, gynecologists, midwives); and 4) other health professionals involved in care for women with hyperemesis gravidarum (general practitioners, dieticians, nurses). To reflect the opinions of the international community, stakeholders from countries in all global regions were invited to participate. RESULTS: Twenty-one identified potential criteria entered the Delphi survey. Of the 277 stakeholders invited, 178 completed round one, and 125 (70%) also completed round two. Twenty stakeholders attended the consensus development meeting, representing all stakeholder groups. The consultation round was completed by 96 (54%) stakeholders, of which 92% agreed with the definition as presented. The consensus definition for hyperemesis gravidarum consisted of: start of symptoms in early pregnancy (before 16 weeks gestational age); nausea and vomiting, at least one of which severe; inability to eat and/or drink normally; strongly limits daily living activities. Signs of dehydration were deemed contributory for the definition for hyperemesis gravidarum. CONCLUSIONS: The proposed definition for hyperemesis gravidarum will help clinical studies to achieve more uniformity, and ultimately increasing the value of evidence to inform patient care.

Hyperbolic enhancement of photocurrent patterns in minimally twisted bilayer graphene.

Quasi-periodic moiré patterns and their effect on electronic properties of twisted bilayer graphene have been intensely studied. At small twist angle θ, due to atomic reconstruction, the moiré superlattice morphs into a network of narrow domain walls separating micron-scale AB and BA stacking regions. We use scanning probe photocurrent imaging to resolve nanoscale variations of the Seebeck coefficient occurring at these domain walls. The observed features become enhanced in a range of mid-infrared frequencies where the hexagonal boron nitride substrate is optically hyperbolic. Our results illustrate the capabilities of the nano-photocurrent technique for probing nanoscale electronic inhomogeneities in two-dimensional materials.

Nanoscale lattice dynamics in hexagonal boron nitride moiré superlattices.

Twisted two-dimensional van der Waals (vdW) heterostructures have unlocked a new means for manipulating the properties of quantum materials. The resulting mesoscopic moiré superlattices are accessible to a wide variety of scanning probes. To date, spatially-resolved techniques have prioritized electronic structure visualization, with lattice response experiments only in their infancy. Here, we therefore investigate lattice dynamics in twisted layers of hexagonal boron nitride (hBN), formed by a minute twist angle between two hBN monolayers assembled on a graphite substrate. Nano-infrared (nano-IR) spectroscopy reveals systematic variations of the in-plane optical phonon frequencies amongst the triangular domains and domain walls in the hBN moiré superlattices. Our first-principles calculations unveil a local and stacking-dependent interaction with the underlying graphite, prompting symmetry-breaking between the otherwise identical neighboring moiré domains of twisted hBN.

Photonic crystal for graphene plasmons.

Photonic crystals are commonly implemented in media with periodically varying optical properties. Photonic crystals enable exquisite control of light propagation in integrated optical circuits, and also emulate advanced physical concepts. However, common photonic crystals are unfit for in-operando on/off controls. We overcome this limitation and demonstrate a broadly tunable two-dimensional photonic crystal for surface plasmon polaritons. Our platform consists of a continuous graphene monolayer integrated in a back-gated platform with nano-structured gate insulators. Infrared nano-imaging reveals the formation of a photonic bandgap and strong modulation of the local plasmonic density of states that can be turned on/off or gradually tuned by the applied gate voltage. We also implement an artificial domain wall which supports highly confined one-dimensional plasmonic modes. Our electrostatically-tunable photonic crystals are derived from standard metal oxide semiconductor field effect transistor technology and pave a way for practical on-chip light manipulation.

Sensitivity of the superconducting state in thin films.

For more than two decades, there have been reports on an unexpected metallic state separating the established superconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it. Here, we show that for two very different thin-film superconductors, amorphous indium oxide and a single crystal of 2H-NbSe2, this metallic state can be eliminated by adequately filtering external radiation. Our results show that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficiently described by the extreme sensitivity of these superconducting films to external perturbations. We relate this sensitivity to the theoretical observation that, in two dimensions, superconductivity is only marginally stable.

Night-time blood pressure patterns and target organ damage: a review.

BACKGROUND: Individuals who do not have a 10% to 20% reduction in blood pressure (BP) during the night are known as 'nondippers'. The cause of this nondipping phenomenon is not fully understood; however, there is a growing body of evidence linking a nondipping BP pattern with target organ damage. OBJECTIVE: To review the literature and present an overview of the target organ damage found to be associated with a nondipping BP pattern. METHODS: PubMed, CINAHL and Medscape searches of all available English language articles from 1986 to 2005 were performed. Search terms included 'BP nondipping', 'BP dipping' and 'target organ damage'. RESULTS: There is evidence to suggest that individuals with hypertension who exhibit a nondipping BP profile are at higher risk of cardiac and extracardiac morbidity and mortality. In particular, nondippers with essential hypertension have been found to have more advanced left ventricular hypertrophy, left ventricular mass and left ventricular mass index, carotid artery wall thickness, carotid artery atherosclerotic plaques, silent cerebral infarct, stroke, cognitive impairment and microalbuminuria. CONCLUSION: A better understanding of the importance of the circadian variations of BP may help to identify those at higher risk of cardiovascular morbidity and mortality, as well as lay the foundation for interventions to prevent/treat alterations in night-time BP patterns.

Even-denominator fractional quantum Hall states in bilayer graphene.

The distinct Landau level spectrum of bilayer graphene (BLG) is predicted to support a non-abelian even-denominator fractional quantum Hall (FQH) state similar to the [Formula: see text] state first identified in GaAs. However, the nature of this state has remained difficult to characterize. Here, we report transport measurements of a robust sequence of even-denominator FQH in dual-gated BLG devices. Parallel field measurement confirms the spin-polarized nature of the ground state, which is consistent with the Pfaffian/anti-Pfaffian description. The sensitivity of the even-denominator states to both filling fraction and transverse displacement field provides new opportunities for tunability. Our results suggest that BLG is a platform in which topological ground states with possible non-abelian excitations can be manipulated and controlled.

Direct measurement of discrete valley and orbital quantum numbers in bilayer graphene.

The high magnetic field electronic structure of bilayer graphene is enhanced by the spin, valley isospin, and an accidental orbital degeneracy, leading to a complex phase diagram of broken symmetry states. Here, we present a technique for measuring the layer-resolved charge density, from which we directly determine the valley and orbital polarization within the zero energy Landau level. Layer polarization evolves in discrete steps across 32 electric field-tuned phase transitions between states of different valley, spin, and orbital order, including previously unobserved orbitally polarized states stabilized by skew interlayer hopping. We fit our data to a model that captures both single-particle and interaction-induced anisotropies, providing a complete picture of this correlated electron system. The resulting roadmap to symmetry breaking paves the way for deterministic engineering of fractional quantum Hall states, while our layer-resolved technique is readily extendable to other two-dimensional materials where layer polarization maps to the valley or spin quantum numbers.The phase diagram of bilayer graphene at high magnetic fields has been an outstanding question, with orders possibly between multiple internal quantum degrees of freedom. Here, Hunt et al. report the measurement of the valley and orbital order, allowing them to directly reconstruct the phase diagram.

Effect of propranolol on plasma norepinephrine during sodium nitroprusside-induced hypotension.

The possibility of an action of propranolol which reduces traffic in the sympathetic nervous system and/or reduces release of norepinephrine at sympathetic nerve endings has been investigated in normal subjects. Plasma norephinephrine was measured in resting supine subjects before and during infusions of sodium nitroprusside which reduced the systolic blood pressure by approximately 10 and later by 20 mm Hg. In 5 subjects these observations were repeated 2 hr after a single 200-mg oral dose of propranolol and in 3 they were repeated after 2 to 8 wk of propranolol 320 mg twice daily. In the control experiments, plasma norepinephrine increased from 0.22 up to 0.74 ng/ml when the blood pressure was reduced by 17/15 mm Hg. Corresponding figures 2 hr after 200 mg propranolol were an increase of plasma norepinephrine from 0.30 or 0.79 ng/ml with a reduction of blood pressure of 19/15 mm Hg. After long-term treatment with 640 mg propranolol daily, a similar reduction of pressure with sodium nitroprusside increased plasma norepinephrine from 0.24 to 0.68 ng/ml. There was no significant alteration in the elevation of plasma norepinephrine following blood pressure reduction with nitroprusside after either short- or long-term treatment with propranolol. These experiments do not suggest a significant role for a nervous system effect of propranolol in modifying sympathetic activity.

Clinical pharmacology and pharmacokinetics of clonidine.

A 300-mug oral dose of clonidine was administered to 5 normal volunteers and measurements of plasma concentration and effects upon blood pressure, heart rate, circulatory reflexes, sedation, and dry mouth were made for the following 8 hr. The plasma concentration rose to a peak of 1.02 +/- 0.52 ng/ml (SD) at 90 min and fell with a mean half-life of 12.7 hr. Blood pressure of the group fell from 111.0/77.0 to 87.2/60.4 after 3 hr and was 95.2/62.2 mm Hg at 8 hr. Heart rate in recumbency was slowed. Marked sedation and a fall in salivary flow followed the same time-course as the plasma concentration. The cold pressor response was reduced but the Valsalva overshoot was little affected.

The wbpM gene in Pseudomonas aeruginosa serogroup O17 resides on a cryptic copy of the serogroup O11 O antigen gene locus.

The Pseudomonas aeruginosa serogroup O11 strain PA103 O antigen gene locus consists of 11 genes designated wzz, wzx, wbjA, wzy, wbjB-F, wbpL, and wbpM. The distribution of each of these genes amongst the 20 P. aeruginosa international antigenic typing system (IATS) serogroups was analyzed by Southern blot. As shown previously, wbpM was present in all 20 serogroups. The remaining O11 O antigen genes, with the exception of wzy, were present in the serogroup O17 strain IATSO17, despite the structural unrelatedness of the O11 and O17 O antigens. Sequencing revealed the presence of a cryptic serogroup O11 locus in the IATSO17 interrupted by two copies of a 1.1-kb insertion element. Introduction of plasmid pLPS2, containing the complete O11 O antigen locus from strain PA103, into IATSO17 resulted in production of both the O11 and O17 O antigens. The results of insertional inactivation of wbpM in IATSO17 are discussed.

Functional modification of indole binding site with indomethacin congeners.

Indomethacin and four congeners were shown by equilibrium dialysis to interfere with the binding of L-tryptophan at the primary indole binding site on defatted human serum albumin. Incubation of albumin with 1-(p-bromoacetamidobenzovl)- and 1-(m-bromoacetamidobenzoyl)-5-methoxy-2-methyl-3-indolylacetic acid functionally modified this site, decreasing the availability of the site for the binding of L-tryptophan. Incubation in the presence of a large excess of L-tryptophan resulted in the partial protection of the site from modification by 1-(m-bromoacetamidobenzoyl)-5-methoxy-2-methyl-3-indolylacetic acid.