Long-range ballistic transport of Brown-Zak fermions in graphene superlattices

In quantizing magnetic fields, graphene superlattices exhibit a complex fractal spectrum often referred to as the Hofstadter butterfly. It can be viewed as a collection of Landau levels that arise from quantization of Brown-Zak minibands recurring at rational (p/q) fractions of the magnetic flux quantum per superlattice unit cell. Here we show that, in graphene-on-boron-nitride superlattices, Brown-Zak fermions can exhibit mobilities above 10⁶ cm² V⁻¹ s⁻¹ and the mean free path exceeding several micrometers. The exceptional quality of our devices allows us to show that Brown-Zak minibands are 4q times degenerate and all the degeneracies (spin, valley and mini-valley) can be lifted by exchange interactions below 1 K. We also found negative bend resistance at 1/q fractions for electrical probes placed as far as several micrometers apart. The latter observation highlights the fact that Brown-Zak fermions are Bloch quasiparticles propagating in high fields along straight trajectories, just like electrons in zero field.

Here, the authors show that Brown-Zak fermions in graphene-on-boron-nitride superlattices exhibit mobilities above 10⁶ cm²/V s and micrometer scale ballistic transport.

Purification of human iPSC-derived cardiomyocytes by HDAC inhibition through inducing apoptosis and cell arrest in non-cardiomyocytes

Background

Cell therapy is one of the most promising strategies for treatment of heart failure. During preparation of iPSC-derived cardiomyocytes for cells therapy, it is important to eliminate the presence of residual proliferative non-target cells in the preparation as these non-target cells could present the risk of tumorgenicity. To minimize the risk, selective and more precise purification process is necessary.

Purpose

We hypothesized that the differences in proliferative activity between cardiomyocytes and non-target cells might result in different sensitivities to the drugs targeting cell growth/survival. The aim of this study is to obtain compounds that eliminate non-cardiomyocytes selectively and to study the mechanism of action of these compounds.

Methods and results

We screened 314 small compounds using both iPSCs and sorted hiPSC-derived cardiomyocytes (hiPSC-CMs). We identified several compounds, which markedly decreased the cell numbers of iPSCs, but showed minimum effects on those of hiPSC-CMs. Among them, HDAC inhibitors were selected as the most promising candidates. We examined whether HDAC inhibitors could purify hiPSC-CMs containing non-cardiomyocytes populations, which were differentiated using the classical embryoid body (EB) method. As a result, HDAC inhibitors increased the purity of cardiomyocytes (up to 98%) by decreasing non-target cells such as smooth muscle cells, endothelial cells, and endodermal lineage cells. Moreover, we confirmed HDAC inhibitors could be used for purification of cardiomyocytes in monolayer differentiation protocol using GSK3β inhibitor and Wnt inhibitor. We measured the expression levels of mRNA and protein in iPSCs and hiPSC-CMs (EB method) treated with HDAC inhibitors. mRNA levels of CDKN1A (p21) and BAX were upregulated in iPSCs. Western blotting analyses revealed that HDAC inhibitors also induced the expression of p21 and the cleavage of Caspase3 in iPSCs.

Conclusions

Our result suggests that the inhibition of HDAC enables an efficient purification of hiPSC-CMs in multiple differentiation methods. Furthermore, our data indicate that HDAC inhibitors induce the apoptosis and cell cycle arrest in iPSCs but not hiPSC-CMs.

Figure 1

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): Takeda Pharmaceutical Company Limited

Sex-related differences in clinical features and in-hospital outcomes of acute aortic dissection type b

Background

Acute aortic dissection (AAD) is a life-threatening medical condition with high morbidity and mortality. The association between female sex and poorer outcomes following surgery for AAD type A has been reported; however, the sex-related differences in clinical features and in-hospital outcomes of AAD type B remain to be elucidated.

Methods

We studied a total of 1877 patients with AAD type B who were enrolled in the Tokyo Acute Aortic Super-network from January 2013 to December 2016. Clinical features and in-hospital outcomes were compared between sexes. Independent predictors of in-hospital mortality were assessed using a multivariable analysis.

Results

The mean age of the patients was 69±13 years and 549 (29%) were females. Female patients were older than males (74±13 years vs 67±13 years; p<0.001). Females had lower systolic blood pressure on admission (158±37 mmHg vs 164±38 mmHg; p=0.007) and were more likely to have altered consciousness level at presentation (8.7% vs 3.9%; p<0.001), intramural hematoma (IMH)-type AAD (62.7% vs 53.6%; p<0.001), and DeBakey type IIIa (28.4% vs 21.8%; p=0.002) compared with males. Females were treated with medical therapy alone more frequently (90.3% vs 85.9%; p=0.009) and had a higher in-hospital mortality rate (5.3% vs 2.6%; p=0.036). A multivariable analysis revealed that age [per year, odds ratio (OR) 1.06; 95% CI 1.04–1.09; p<0.001], altered consciousness level (OR 3.28; 95% CI 1.54–6.98; p=0.002), shock/hypotension (OR 14.0; 95% CI 5.92–33.1; p<0.001), classic-type AAD (OR 2.54; 95% CI 1.36–4.73; p=0.003), and medical therapy alone (OR 0.28; 95% CI 0.15–0.54; p<0.001) were independent predictors of in-hospital mortality, whereas female sex was not predictive of in-hospital mortality (OR 1.64; 95% CI 0.91–2.96; p=0.10).

Conclusion

In AAD type B, females were older and had altered consciousness level, IMH-type, and a less widespread dissection more frequently than males. The overall in-hospital mortality was higher in females; however, female sex was not associated with in-hospital mortality after multivariable adjustment.

Funding Acknowledgement

Type of funding source: None

Diagnostic markers for discriminating between acute aortic dissection and acute myocardial infarction during the pre-hospital phase: analysis of 3,195 cases

 

Both acute aortic dissection (AAD) and acute myocardial infarction (AMI) present with chest pain and are life-threatening diseases that require early diagnosis and treatment for better clinical outcome. However, two critical diseases in the very acute phase are sometimes difficult to differentiate, especially prior to arrival at the hospital for urgent diagnosis and selection of specific treatment.

The aim of our study was to clarify the diagnostic markers acquired from the information gathered from medical history taking and physical examination for discriminating AAD from AMI by using data from the Tokyo Cardiovascular Care Unit (CCU) Network database.

We examined the clinical features and laboratory data of patients with AAD and AMI who were admitted to the hospital in Tokyo between January 2013 and December 2015 by using the Tokyo CCU Network database. The Tokyo CCU Network consists of >60 hospitals that fulfil certain clinical criteria and receive patients from ambulance units coordinated by the Tokyo Fire Department. Of 15,061 patients diagnosed as having AAD and AMI, 3,195 with chest pain within 2 hours after symptom onset (537 AAD and 2,658 AMI) were examined. The patients with out-of-hospital cardiac arrest were excluded.

We compared the clinical data of the patients with chest pain who were diagnosed as having AAD and AMI. The following indicators were more frequent or had higher values among those with AAD: female sex (38% vs. 20%, P<0.001), systolic blood pressures (SBPs) at the time of first contact by the emergency crew (142 mmHg vs. 127 mmHg), back pain in addition to chest pain (54% vs. 5%, P<0.001), history of hypertension (73% vs. 58%, P<0.001), SBP ≥150 mmHg (39% vs. 22%, P<0.001), back pain combined with SBP ≥150 mmHg (23% vs. 0.8%, P<0.001), and back pain with SBP <90 mmHg (4.5% vs. 0.1%, P<0.001). The following data were less frequently observed among those with AAD: diabetes mellitus (7% vs. 28%, P<0.001), dyslipidaemia (17% vs. 42%, P<0.001), and history of smoking (48% vs. 61%, P<0.001). The multivariate regression analysis suggested that back pain with SBP ≥150 mmHg (odds ratio [OR] 47; 95% confidence interval [CI] 28–77; P<0.001), back pain with SBP <90 mmHg (OR 68, 95% CI 16–297, P<0.001), and history of smoking (OR 0.49, 95% CI 0.38–0.63, P<0.001) were the independent markers of AAD. The sensitivity and specificity of back pain with SBPs of ≥150 mmHg and back pain with SBPs <90 mmHg for detecting AAD were 23% and 99%, and 4% and 99%, respectively.

In patients with chest pain suspicious of AAD and AMI, “back pain accompanied by chest pain with SBP ≥150 mmHg” or “back pain accompanied by chest pain with SBP <90 mmH” is a reliable diagnostic marker of AAD with high specificity, although the sensitivity was low. The two SBP values with back pain are markers that may be useful for the ambulance crew at their first contact with patients with chest pain.

Funding Acknowledgement

Type of funding source: None

A comparison of rate control and rhythm control in tachycardia induced cardiomyopathy patients with persistent atrial flutter

Background/Introduction

Tachycardia induced cardiomyopathy (TIC) is a potentially reversible dysfunction of the left ventricle (LV) caused by tachyarrhythmias. Early recognition of TIC and treatment of the culprit arrhythmia using pharmacological therapy or catheter ablation results in the recovery of LV function. For atrial flutter (AFL)-induced TIC, rhythm control strategy, such as catheter ablation has been recommended. On the other hand, the efficacy of rate control strategy has remained unclear due to the difficulty of control with arrhythmic medications. However, not all patients can take rhythm control treatments due to their backgrounds.

Purpose

The aim of this cohort study was to establish whether rate control strategy using β-blocker is as effective as invasive rhythm control strategy for the recovery of LV function in patients with TIC due to AFL.

Methods

We prospectively assessed 47 symptomatic non-ischaemic heart failure (HF) patients with left ventricular ejection fraction (LVEF) below 50% and suspected TIC induced by persistent AFL. Patients were divided into rhythm control strategy group (n=22, treatment: catheter ablation, electrical cardioversion) and rate control strategy group (n=25, treatment: bisoprolol). As a sub-group study, the rate control strategy group was divided into the strict rate control group (n=12, average heart rate below 80 bpm) and lenient rate control group (n=13, average heart rate below 110 bpm). The primary outcome was the recovery of LV function, defined as an increase of LVEF over 20% or to a value of 55% or greater after 6 months.

Results

There were no significant differences in baseline AFL heart rate, New York Heart Association class, LVEF, estimated glomerular filtration rate, and brain natriuretic peptide between the two groups. A greater proportion of patients who showed the recovery of LVEF after 6 months belonged to the rhythm control strategy group (90.9% vs. 52.0%, p=0.004). The cumulative incidence of HF re-hospitalization was significantly higher in the rate control strategy group than in the rhythm control strategy group (hazard ratio: 4.90, 95% CI: 1.06–22.69). As a result of sub-group study, LVEF recovery was greater in the strict rate control group compared to the lenient rate control group (75.0% vs. 30.8%, p=0.027)

Conclusion

Rate control strategy was significantly inferior to rhythm control strategy for the recovery of LVEF in TIC patients with persistent AFL. Rhythm control should be the first choice in the management of TIC with AFL, and strict rate control should be an alternative if rhythm control is not available.

Primary outcomes

Funding Acknowledgement

Type of funding source: None

Electron-Hole Crossover in Gate-Controlled Bilayer Graphene Quantum Dots

Electron and hole Bloch states in bilayer graphene exhibit topological orbital magnetic moments with opposite signs, which allows for tunable valley-polarization in an out-of-plane magnetic field. This property makes electron and hole quantum dots (QDs) in bilayer graphene interesting for valley and spin-valley qubits. Here, we show measurements of the electron-hole crossover in a bilayer graphene QD, demonstrating opposite signs of the magnetic moments associated with the Berry curvature. Using three layers of top gates, we independently control the tunneling barriers while tuning the occupation from the few-hole regime to the few-electron regime, crossing the displacement-field-controlled band gap. The band gap is around 25 meV, while the charging energies of the electron and hole dots are between 3 and 5 meV. The extracted valley g-factor is around 17 and leads to opposite valley polarization for electrons and holes at moderate B-fields. Our measurements agree well with tight-binding calculations for our device.

Neutral and charged dark excitons in monolayer WS2

Low temperature and polarization resolved magneto-photoluminescence experiments are used to investigate the properties of dark excitons and dark trions in a monolayer of WS2 encapsulated in hexagonal BN (hBN). We find that this system is an n-type doped semiconductor and that dark trions dominate the emission spectrum. In line with previous studies on WSe2, we identify the Coulomb exchange interaction coupled neutral dark and grey excitons through their polarization properties, while an analogous effect is not observed for dark trions. Applying the magnetic field in both perpendicular and parallel configurations with respect to the monolayer plane, we determine the g-factor of dark trions to be g ∼ -8.6. Their decay rate is close to 0.5 ns, more than 2 orders of magnitude longer than that of bright excitons.

Effects of royal jelly on bone metabolism in postmenopausal women: a randomized, controlled study

OBJECTIVES

This study aimed to evaluate the effects of royal jelly (RJ) supplementation on bone metabolism in postmenopausal women.

METHODS

This was a randomized, double-blind, placebo-controlled clinical trial. Seventy-two healthy postmenopausal women aged 45-60 years within 5 years after menopause were randomized into two groups: women in the RJ group (n = 36) received capsules containing dried RJ (equivalent to 3000 mg of fresh RJ); and women in the placebo group (n = 36) received placebo daily for 6 months. Bone mineral density (BMD) of the lumbar spine (L2-L4) and left proximal femur, hip structural analysis (HSA) of the left hip, and bone turnover markers were measured.

RESULTS

Although women in the placebo group experienced a significant loss of BMD and deterioration in HSA parameters of the femur, no significant differences were found in these parameters in women in the RJ group. The levels of total procollagen type 1 N-terminal propeptide (P1NP) and tartrate-resistant acid phosphatase decreased significantly in the placebo group; however, the total P1NP level, a marker of bone formation, was not significantly different in the RJ group at postintervention compared with baseline.

CONCLUSION

RJ consumption may ameliorate decreases in femoral BMD and strength in postmenopausal women.

Highly energy-tunable quantum light from moiré-trapped excitons

Photon antibunching, a hallmark of quantum light, has been observed in the correlations of light from isolated atomic and atomic-like solid-state systems. Two-dimensional semiconductor heterostructures offer a unique method to create a quantum light source: Moiré trapping potentials for excitons are predicted to create arrays of quantum emitters. While signatures of moiré-trapped excitons have been observed, their quantum nature has yet to be confirmed. Here, we report photon antibunching from single moiré-trapped interlayer excitons in a heterobilayer. Via magneto-optical spectroscopy, we demonstrate that the discrete anharmonic spectra arise from bound band-edge electron-hole pairs trapped in moiré potentials. Last, we exploit the large permanent dipole of interlayer excitons to achieve large direct current (DC) Stark tuning up to 40 meV. Our results confirm the quantum nature of moiré-confined excitons and open opportunities to investigate their inhomogeneity and interactions between the emitters or energetically tune single emitters into resonance with cavity modes.

Relationship between Histological Grade and Histopathological Appearance in Canine Mammary Carcinomas

Canine mammary carcinomas are common tumours in female dogs and histopathological examination has an important role in identifying whether they are benign or malignant. The latest and most commonly used histological grading system was established by Peña et al. (2013) and is based on the extent of tubule formation, nuclear pleomorphism and number of mitoses. Before the establishment of this grading system, tumour size and classical histological indicators of malignancy such as lymphovascular invasion, infiltration into surrounding tissue, necrosis and presence of a micropapillary pattern were important predictors of biological behaviour. However, the system of Peña et al. does not consider tumour size or these histological features. Clarifying the association of these features and histological grade, especially in grade II and III carcinomas, is important. In this study, we confirmed that the system of Peña et al. is effective for predicting biological behaviour and that evaluation of histological features of malignancy reinforced histological grade, as determined by the system of Peña et al., especially in grade II carcinomas.

Measurement of the spin-forbidden dark excitons in MoS2 and MoSe2 monolayers

Excitons with binding energies of a few hundreds of meV control the optical properties of transition metal dichalcogenide monolayers. Knowledge of the fine structure of these excitons is therefore essential to understand the optoelectronic properties of these 2D materials. Here we measure the exciton fine structure of MoS2 and MoSe2 monolayers encapsulated in boron nitride by magneto-photoluminescence spectroscopy in magnetic fields up to 30 T. The experiments performed in transverse magnetic field reveal a brightening of the spin-forbidden dark excitons in MoS2 monolayer: we find that the dark excitons appear at 14 meV below the bright ones. Measurements performed in tilted magnetic field provide a conceivable description of the neutral exciton fine structure. The experimental results are in agreement with a model taking into account the effect of the exchange interaction on both the bright and dark exciton states as well as the interaction with the magnetic field.

Predictors of radiological aggravations of pulmonary MAC disease

Background and objectives

The number of patients with pulmonary Mycobacterium avium complex (MAC) disease is increasing worldwide, especially among middle-aged women and never-smokers.

However, little is known about the factors causing exacerbations of pulmonary MAC disease in untreated patients. The aim of the present study was to identify the predictors of radiological aggravations of pulmonary MAC disease.

Methods

From April 2011 to December 2018, 238 MAC patients at our institute were newly diagnosed with pulmonary MAC disease according to the 2007 American Thoracic Society/Infectious Disease Society guideline. Their medical records were examined retrospectively for their clinical findings. The radiological findings at the time of the diagnosis and 1 year later were evaluated. To identify the predictors of radiological aggravation, multivariable analysis was performed with the data of 167 treatment-naïve patients.

Results

Female, never-smoker, and nodular/bronchiectatic (NB) type were predominant in patients with pulmonary MAC disease. Univariate analysis of data from treatment-naïve subjects showed that no lung diseases other than MAC, extensive radiological findings, and a positive acid-fast bacilli (AFB) smear were significantly associated with radiological aggravations. On multivariate analysis, the radiological factor (larger affected area) and absence of other lung disease were significantly associated with radiological aggravations. In particular, the presence of abnormal shadows in more than 3 lobes was significantly associated with radiological aggravations.

Conclusions

In this study, the presence of extensive radiological findings and the absence of lung diseases other than MAC were predictors of radiological aggravations of treatment-naïve pulmonary MAC disease. In particular, the presence of abnormal shadows in more than 3 lobes was significantly associated with radiological aggravations.

Erratum: Evolution of π^{0} Suppression in Au+Au Collisions from sqrt[s_{NN}]=39 to 200 GeV [Phys. Rev. Lett. 109, 152301 (2012)]

This corrects the article DOI: 10.1103/PhysRevLett.109.152301.

Demonstration of a polariton step potential by local variation of light-matter coupling in a van-der-Waals heterostructure

The large oscillator strength of excitons in transition metal dichalcogenide layers facilitates the formation of exciton-polariton resonances for monolayers and van-der-Waals heterostructures embedded in optical microcavities. Here, we show, that locally changing the number of layers in a WSe₂/hBN/WSe₂ van-der-Waals heterostructure embedded in a monolithic, high-quality-factor cavity gives rise to a local variation of the coupling strength. This effect yields a polaritonic stair case potential, which we demonstrate at room temperature. Our result paves the way towards engineering local polaritonic potentials at length scales down to atomically sharp interfaces, based on purely modifying its real part contribution via the coherent light-matter coupling strength g.

Cascade of phase transitions and Dirac revivals in magic-angle graphene

Twisted bilayer graphene near the magic angle^1-4 exhibits rich electron-correlation physics, displaying insulating^3-6, magnetic^7,8 and superconducting phases^4-6. The electronic bands of this system were predicted^1,2 to narrow markedly^9,10 near the magic angle, leading to a variety of possible symmetry-breaking ground states^11-17. Here, using measurements of the local electronic compressibility, we show that these correlated phases originate from a high-energy state with an unusual sequence of band population. As carriers are added to the system, the four electronic 'flavours', which correspond to the spin and valley degrees of freedom, are not filled equally. Rather, they are populated through a sequence of sharp phase transitions, which appear as strong asymmetric jumps of the electronic compressibility near integer fillings of the moiré lattice. At each transition, a single spin/valley flavour takes all the carriers from its partially filled peers, 'resetting' them to the vicinity of the charge neutrality point. As a result, the Dirac-like character observed near charge neutrality reappears after each integer filling. Measurement of the in-plane magnetic field dependence of the chemical potential near filling factor one reveals a large spontaneous magnetization, further substantiating this picture of a cascade of symmetry breaking. The sequence of phase transitions and Dirac revivals is observed at temperatures well above the onset of the superconducting and correlated insulating states. This indicates that the state that we report here, with its strongly broken electronic flavour symmetry and revived Dirac-like electronic character, is important in the physics of magic-angle graphene, forming the parent state out of which the more fragile superconducting and correlated insulating ground states emerge.

Observation of the Spin-Orbit Gap in Bilayer Graphene by One-Dimensional Ballistic Transport

We report on measurements of quantized conductance in gate-defined quantum point contacts in bilayer graphene that allow the observation of subband splittings due to spin-orbit coupling. The size of this splitting can be tuned from 40 to 80  μeV by the displacement field. We assign this gate-tunable subband splitting to a gap induced by spin-orbit coupling of Kane-Mele type, enhanced by proximity effects due to the substrate. We show that this spin-orbit coupling gives rise to a complex pattern in low perpendicular magnetic fields, increasing the Zeeman splitting in one valley and suppressing it in the other one. In addition, we observe a spin polarized channel of 6e^{2}/h at high in-plane magnetic field and signatures of interaction effects at the crossings of spin-split subbands of opposite spins at finite magnetic field.

Persistent tobacco smoke residue in multiunit housing: Legacy of permissive indoor smoking policies and challenges in the implementation of smoking bans

Secondhand smoke (SHS) is a common indoor pollutant in multiunit housing (MUH). It is also the precursor of thirdhand smoke (THS), the toxic mixture of tobacco smoke residue that accumulates in indoor environments where tobacco has been used. This study examined the levels, distribution, and factors associated with THS pollution in low-income MUH. Interviews were conducted 2016-2018 in a cross-sectional study of N = 220 MUH homes in San Diego, California. Two surface wipe samples were collected per home and analyzed for nicotine, a THS marker, using liquid chromatography-triple quadrupole mass spectrometry. Nicotine was detected in all homes of nonsmokers with indoor smoking bans (Geo Mean = 1.67 µg/m²; 95% CI = [1.23;2.30]) and smokers regardless of an indoor ban (Geo Mean = 4.80 µg/m²; 95% CI = [1.89;12.19]). Approximately 10% of nonsmokers' homes with smoking bans showed nicotine levels higher than the average level in homes of smokers without smoking bans from previous studies (≥30 µg/m²). Housing for seniors, smoking bans on balconies, indoor tobacco use, difficult to reach surfaces, and self-reported African-American race/ethnicity were independently associated with higher THS levels. Individual cases demonstrated that high levels of surface nicotine may persist in nonsmoker homes for years after tobacco use even in the presence of indoor smoking bans. To achieve MUH free of tobacco smoke pollutants, attention must be given to identifying and remediating highly polluted units and to implementing smoking policies that prevent new accumulation of THS. As THS is a form of toxic tobacco product waste, responsibility for preventing and mitigating harmful impacts should include manufacturers, suppliers, and retailers.

Minibands in twisted bilayer graphene probed by magnetic focusing

Magnetic fields force ballistic electrons injected from a narrow contact to move along skipping orbits and form caustics. This leads to pronounced resistance peaks at nearby voltage probes as electrons are effectively focused inside them, a phenomenon known as magnetic focusing. This can be used not only for the demonstration of ballistic transport but also to study the electronic structure of metals. Here, we use magnetic focusing to probe narrowbands in graphene bilayers twisted at ~2°. Their minibands are found to support long-range ballistic transport limited at low temperatures by intrinsic electron-electron scattering. A voltage bias between the layers causes strong minivalley splitting and allows selective focusing for different minivalleys, which is of interest for using this degree of freedom in frequently discussed valleytronics.

Localized Nanoresonator Mode in Plasmonic Microcavities

Submicron-thick hexagonal boron nitride crystals embedded in noble metals form planar Fabry-Perot half-microcavities. Depositing Au nanoparticles on top of these microcavities forms previously unidentified angle- and polarization-sensitive nanoresonator modes that are tightly laterally confined by the nanoparticle. Comparing dark-field scattering with reflection spectroscopies shows plasmonic and Fabry-Perot-like enhancements magnify subtle interference contributions, which lead to unexpected redshifts in the dark-field spectra, explained by the presence of these new modes.

Ultra-long carrier lifetime in neutral graphene-hBN van der Waals heterostructures under mid-infrared illumination

Graphene/hBN heterostructures are promising active materials for devices in the THz domain, such as emitters and photodetectors based on interband transitions. Their performance requires long carrier lifetimes. However, carrier recombination processes in graphene possess sub-picosecond characteristic times for large non-equilibrium carrier densities at high energy. An additional channel has been recently demonstrated in graphene/hBN heterostructures by emission of hBN hyperbolic phonon polaritons (HPhP) with picosecond decay time. Here, we report on carrier lifetimes in graphene/hBN Zener-Klein transistors of ~30 ps for photoexcited carriers at low density and energy, using mid-infrared photoconductivity measurements. We further demonstrate the switching of carrier lifetime from ~30 ps (attributed to interband Auger) down to a few picoseconds upon ignition of HPhP relaxation at finite bias and/or with infrared excitation power. Our study opens interesting perspectives to exploit graphene/hBN heterostructures for THz lasing and highly sensitive THz photodetection as well as for phonon polariton optics.

Long carrier lifetimes are beneficial for graphene-based optoelectronics, but carrier recombination processes in graphene possess sub-picosecond characteristic times. Here, the authors report carrier lifetimes ~30 ps at low energy in graphene/hBN Zener-Klein transistors, attributed to interband Auger processes.

Achievement of high power and long pulse negative ion beam acceleration for JT-60SA NBI

Long pulse acceleration of hydrogen negative ion beams with the power density over 70 MW/m² and the pulse length over 100 s has been demonstrated for the first time by using a multi-aperture 3-stage accelerator. Such long pulse acceleration was achieved by integrating the design of beam optics and voltage holding capability to meet the requirements of JT-60SA. By using the newly designed accelerator for JT-60SA, voltage holding at 500 kV with beam acceleration was stably sustained even after 5 g of cesium was seeded, and heat load on each acceleration grid was reduced below the allowable level for long pulse, less than 5% of total acceleration power. As a result, 500 keV, 154 A/m² for 118 s beam acceleration was achieved, which satisfies the requirement of the negative ion source for JT-60SA. This pulse length of such high-power density beams is longest in the world. In addition, the result contributes to the long pulse acceleration of multi-stage electrostatic accelerators, such as 1 MeV negative ion accelerator for ITER.

Dentoalveolar Defects in the Hyp Mouse Model of X-linked Hypophosphatemia

Mutations in PHEX cause X-linked hypophosphatemia (XLH), a form of hypophosphatemic rickets. Hyp (Phex mutant) mice recapitulate the XLH phenotype. Dental disorders are prevalent in individuals with XLH; however, underlying dentoalveolar defects remain incompletely understood. We analyzed Hyp mouse dentoalveolar defects at 42 and 90 d postnatal to comparatively define effects of XLH on dental formation and function. Phex mRNA was expressed by odontoblasts (dentin), osteocytes (bone), and cementocytes (cellular cementum) in wild-type (WT) mice. Enamel density was unaffected, though enamel volume was significantly reduced in Hyp mice. Dentin defects in Hyp molars were indicated histologically by wide predentin, thin dentin, and extensive interglobular dentin, confirming micro-computed tomography (micro-CT) findings of reduced dentin volume and density. Acellular cementum was thin and showed periodontal ligament detachment. Mechanical testing indicated dramatically altered periodontal mechanical properties in Hyp versus WT mice. Hyp mandibles demonstrated expanded alveolar bone with accumulation of osteoid, and micro-CT confirmed decreased bone volume fraction and alveolar bone density. Cellular cementum area was significantly increased in Hyp versus WT molars owing to accumulation of hypomineralized cementoid. Histology, scanning electron microscopy, and nanoindentation revealed hypomineralized "halos" surrounding Hyp cementocyte and osteocyte lacunae. Three-dimensional micro-CT analyses confirmed larger cementocyte/osteocyte lacunae and significantly reduced perilacunar mineral density. While long bone and alveolar bone osteocytes in Hyp mice overexpressed fibroblast growth factor 23 (Fgf23), its expression in molars was much lower, with cementocyte Fgf23 expression particularly low. Expression and distribution of other selected markers were disturbed in Hyp versus WT long bone, alveolar bone, and cementum, including osteocyte/cementocyte marker dentin matrix protein 1 (Dmp1). This study reports for the first time a quantitative analysis of the Hyp mouse dentoalveolar phenotype, including all mineralized tissues. Novel insights into cellular cementum provide evidence for a role for cementocytes in perilacunar mineralization and cementum biology.

A retrospective clinical research of relapsed organizing pneumonia

BACKGROUND

Organizing pneumonia (OP) usually responds spectacularly well to initial treatment, but relapses can occur and some cases run a fatal course. Still, the issue of relapse has been addressed in relatively few studies, and predictors have not been clarified. The purpose of this study was to examine the pattern of relapses in OP, to determine whether relapse affects morbidity and mortality, and to identify possible predictors of relapse.

METHODS

Blood sampling, pulmonary function testing, computed tomography (CT) of the chest, and bronchofiberscopy were performed for all patients and were retrospectively reviewed along with clinical information. Periodical chest CT was conducted and additional chest CT was performed when relapse of OP was clinically suspected. All patients were followed regarding treatment response, treatment duration, and presence of relapse. Results were compared between two groups based on serum concentrations of surfactant protein (SP)-D: normal SP-D and high SP-D.

RESULTS

Twenty-two patients were analyzed in this study. SP-D showed a negative correlation with percutaneous oxygen saturation and positive correlations with serum lactate dehydrogenase, Krebs von den Lungen (KL)-6, and percentage of lymphocytes in bronchoalveolar lavage (BAL). Prognosis was good for all patients, but relapse was significantly more frequent in the high SP-D group (6 cases) than in the normal SP-D group (0 cases; P = 0.049). Serum KL-6 and percentage of monocytes in BAL were significantly higher, and pulmonary vital capacity and forced expiratory volume in 1 s were significantly lower in the high SP-D group than in the low SP-D group.

CONCLUSIONS

When treating cases of OP with high serum concentrations of SP-D, attention should be paid to the possibility of relapse.

Organic contaminants in human breast milk identified by non-targeted analysis

Understanding the health implications of human exposure to mixtures of chemical contaminants is aided by analytical methods that can screen for a broad range of both expected and unexpected compounds. We performed a proof-of-concept analysis combining human breast milk, a biomonitoring matrix for determining contaminant exposure to mothers and infants, with a non-targeted method based on comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOF-MS). A total of 172 presumably anthropogenic halogenated compounds and non-halogenated cyclic and aromatic compounds were tentatively identified in breast milk from San Diego, California through mass spectral database searches. Forty of the compounds were prioritized for confirmation based on halogenation or 100% frequency of detection, and the identities of 30 were verified using authentic standards. Thirty-four (85%) of the prioritized contaminants are not typically monitored in breast milk surveys, and 31 (77%) are regulated in at least one market worldwide, indicating breast milk may be a useful biomonitoring matrix for non-targeted analysis and the assessment of human exposure to future emerging or undiscovered contaminants.

Intrinsic quantized anomalous Hall effect in a moiré heterostructure

The quantum anomalous Hall (QAH) effect combines topology and magnetism to produce precisely quantized Hall resistance at zero magnetic field. We report the observation of a QAH effect in twisted bilayer graphene aligned to hexagonal boron nitride. The effect is driven by intrinsic strong interactions, which polarize the electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1. In contrast to magnetically doped systems, the measured transport energy gap is larger than the Curie temperature for magnetic ordering, and quantization to within 0.1% of the von Klitzing constant persists to temperatures of several kelvin at zero magnetic field. Electrical currents as small as 1 nanoampere controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.

Composite super-moiré lattices in double-aligned graphene heterostructures

When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moiré pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moiré patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moiré pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moiré super cell.

Social relationships and functional status among Japanese elderly adults living in a suburban area

OBJECTIVES

Social relationships may help in maintaining functional status among older adults. This study examined the types of social relationships that were related to functional status among Japanese community-dwelling older adults.

STUDY DESIGN

This is a prospective cohort study.

METHODS

We used baseline data from 2008 and conducted follow-up surveys six years later. Participants included individuals older than 65 years who lived in a suburban community in Japan. The Index of Social Interaction measure was used to assess multiple elements of social relationships. Two functional status outcomes were set: (1) functional decline and (2) functional decline and mortality. A multiple logistic regression model was used to examine the association between social relationships and functional decline six years later.

RESULTS

After controlling for age, sex, family structure and disease status in 2008, poor social curiosity (odds ratio [OR] = 1.31, 95% confidence interval [CI]: 1.02-1.69) and interaction (OR = 2.57, 95% CI: 1.20-5.51) were found to be associated with functional decline. Furthermore, social curiosity (OR = 1.39, 95% CI: 1.14-1.69) and interaction (OR = 2.84, 95% CI: 1.44-5.59) were also associated with the composite outcome.

CONCLUSIONS

Social curiosity and interacting with others were significantly associated with functional status. Promotion of social interaction may be essential for preventing future need for care.

Determination of Docosahexaenoic Acid and n-3 Fatty Acids in Refined Fish Oils by H-NMR Spectroscopy: IUPAC Interlaboratory Study

A high-resolution proton nuclear magnetic resonance (NMR) method for determining the concentration (mg/g) of docosahexaenoic acid (DHA), the molar proportion (mol%) of DHA, and the molar proportion of total n-3 fatty acids in fish oils was validated by an IUPAC interlaboratory study (the Commission VI-6 on Oils, Fats, and Derivatives WG 3/98). Thirteen laboratories from 5 countries tested 6 pairs of blind duplicate fish oils: a refined tuna oil, 2 extracted tuna oils, an extracted bonito oil, an extracted salmon oil, and an extracted sardine oil ranging from 9 to 30 mol% DHA and from 20 to 35 mol% n-3 fatty acids. Before 1D-proton NMR measurements with 300–500 MHz instruments, oil samples were weighed and diluted with deuterochloroform solution containing ethylene glycol dimethyl ether as internal standard. To achieve precise performance, a detailed procedure for signal area measurement was described in the protocol, and all participants were instructed about the critical importance of following the protocol. Statistical performances with invalid and outlier data removed were as follows: repeatability relative standard deviations (RSDr) ranged from 0.91 to 2.62% and reproducibility relative standard deviation (RSDR) ranged from 1.73 to 4.27% for DHA concentration (mg/g); RSDr ranged from 0.39 to 2.06%, and RSDR ranged from 0.59 to 3.46% for mol% DHA; RSDr ranged from 0.23 to 0.90% and RSDR ranged from 0.85 to 2.01% for mol% total n-3 fatty acids. The method is expected to be recommended by IUPAC.

Secretory IgA accumulated in the airspaces of idiopathic pulmonary fibrosis and promoted VEGF, TGF-β and IL-8 production by A549 cells

Secretory IgA (SIgA) is a well-known mucosal-surface molecule in first-line defense against extrinsic pathogens and antigens. Its immunomodulatory and pathological roles have also been emphasized, but it is unclear whether it plays a pathological role in lung diseases. In the present study, we aimed to determine the distribution of IgA in idiopathic pulmonary fibrosis (IPF) lungs and whether IgA affects the functions of airway epithelial cells. We performed immunohistochemical analysis of lung sections from patients with IPF and found that mucus accumulated in the airspaces adjacent to the hyperplastic epithelia contained abundant SIgA. This was not true in the lungs of non-IPF subjects. An in-vitro assay revealed that SIgA bound to the surface of A549 cells and significantly promoted production of vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β and interleukin (IL)-8, important cytokines in the pathogenesis of IPF. Among the known receptors for IgA, A549 cells expressed high levels of transferrin receptor (TfR)/CD71. Transfection experiments with siRNA targeted against TfR/CD71 followed by stimulation with SIgA suggested that TfR/CD71 may be at least partially involved in the SIgA-induced cytokine production by A549 cells. These phenomena were specific for SIgA, distinct from IgG. SIgA may modulate the progression of IPF by enhancing synthesis of VEGF, TGF-β and IL-8.

Tunable crystal symmetry in graphene-boron nitride heterostructures with coexisting moiré superlattices

In van der Waals (vdW) heterostructures consisting of atomically thin crystals layered on top of one another, lattice mismatch and rotation between the layers can result in long-wavelength moiré superlattices. These moiré patterns can drive notable band structure reconstruction of the composite material, leading to a wide range of emergent phenomena including superconductivity^1-3, magnetism⁴, fractional Chern insulating states⁵ and moiré excitons^6-9. Here, we investigate devices consisting of monolayer graphene encapsulated between two crystals of boron nitride (BN), in which the rotational alignment of all three components is controlled. We find that bandgaps in the graphene arising from perfect rotational alignment with both BN layers can be modified considerably depending on whether the relative orientation of the two BN layers is 0° or 60°, suggesting a tunable transition between the absence or presence of inversion symmetry in the heterostructure. Small deviations (<1°) from perfect alignment of all three layers leads to coexisting long-wavelength moiré potentials, resulting in a highly reconstructed graphene band structure featuring multiple secondary Dirac points. Our results demonstrate that the interplay between multiple moiré patterns can be utilized to controllably modify the symmetry and electronic properties of the composite heterostructure.

P1227Remnant lipoprotein is a residual risk of future cardiovascular events in patients with stable coronary artery disease and on statin LDL-cholesterol levels less than 70 mg/dl

Background

Recent guidelines recommend a target of low density lipoprotein cholesterol (LDL-C) <70 mg/dL in patients at very high risk of cardiovascular disease (CVD). However, a considerable residual risk of CVD persists despite achievement of the LDL-C goal on statin treatment.

Purpose

This study examined the predictive value of remnant lipoprotein levels for cardiovascular events (CVE) in patients with stable coronary artery disease (CAD) and LDL-C levels <70 mg/dL on statin treatment.

Methods

Serum levels of remnant lipoproteins (remnant-like lipoprotein particles cholesterol; RLP-C) were measured by an immunoseparation method in 247 consecutive patients with CAD who had on-statin LDL-C levels <70 mg/dL. All the patients were followed prospectively for a period of ≤60 months or until the occurrence of the primary composite endpoint of cardiac death, nonfatal myocardial infarction, unstable angina requiring coronary revascularization, worsening heart failure, peripheral artery diseases requiring endovascular or surgical intervention, aortic events, and ischemic stroke.

Results

During a mean follow-up period of 38 months, 33 CVEs occurred. Kaplan-Meier estimates in time-to-first-event analysis demonstrated that higher RLP-C levels (>3.9 mg/dL, determined by ROC-curve) resulted in a significantly higher probability for the primary endpoint than did lower RLP-C levels (<3.9 mg/dL) (p<0.01 by log-rank test). Stepwise multivariate Cox proportional hazard analysis showed that RLP-C was a significant predictor of the primary endpoint after adjustment for known risk factors and lipid variables including triglycerides (TG), and total apolipoprotein B (ApoB) (HR 1.62, 95% CI 1.26–2.07, p<0.01). The c-statistics showed that addition of RLP-C had a significant incremental effect on the predictive value of traditional risk factors (area under curve; traditional risk factors: 0.68 vs. traditional risk factors + RLP-C: 0.77, p=0.02). Category-free NRI and IDI demonstrated the additive value of RLP-C to the traditional risk factors plus non-high-density lipoprotein (HDL)-C and ApoB levels (NRI 0.52, p<0.01; IDI 0.06, p<0.01).

Conclusions

RLP-C levels are a residual risk factor for future CVEs in patients with CAD and on-statin LDL-C <70 mg/dL.

129Elevated plasma xanthine oxidoreductase activity predicts cardiovascular events in patients with heart failure with preserved ejection fraction

Background

The pathophysiology of heart failure with preserved ejection fraction (HFpEF) remains poorly understood, although reactive oxygen species (ROS) is reportedly involved in underlying mechanisms. Xanthine oxidoreductase (XOR) is the rate-limiting enzyme of purine metabolism that plays an important role in producing uric acid, and also generates the ROS. However, the impact of plasma XOR activity on the clinical outcomes in patients with HFpEF remains unclear.

Purpose

The aim of this study was to assess whether plasma XOR activity predicts cardiovascular events in patients with HFpEF.

Methods and results

We measured plasma XOR activity in 257 patients with HFpEF. The patients were divided into 3 groups based on XOR activity: low XOR group (<33 pmol/h/mL, n=45), normal XOR group (33 - 120 pmol/h/mL, n=160), and high XOR group (≥120 pmol/h/mL, n=52). During a median follow-up period of 809 days, there were 74 major adverse cardiovascular events (MACEs). Kaplan-Meier analysis demonstrated that the patients with high XOR activity were at greatest risk for MACEs. A multivariate Cox proportional hazard regression analysis showed that high XOR activity was significantly associated with MACEs after adjustment for confounding factors. Furthermore, we divided the patients into 4 groups according to the presence of high XOR activity and/or hyperuricemia. Cox multivariate hazard regression analysis revealed that the patients with high XOR activity were associated with cardiovascular events in patients with HFpEF, regardless of whether hyperuricemia was present or not.

Conclusions

Elevated plasma XOR activity is significantly associated with adverse clinical outcomes in patients with HFpEF. Inhibition of XOR could be a potential therapy for HFpEF.

P1626MicroRNA-21 deteriorates left ventricular reverse remodeling by promoting cardiac fibrosis in non-ischemic cardiomyopathy

Background

Left ventricular reverse remodeling (LVRR) contributes to better outcomes in patients with non-ischemic cardiomyopathy (NICM). It is reported that LVRR is associated with progression of cardiac fibrosis. MicroRNAs (miRs) have emerged as powerful regulators of post-transcriptional gene expression. We focused on miR-21, which plays a key role in pathogenesis of fibrosis in multiple organs. The aim of this study was to clarify the effect of miR-21 on cardiac fibrosis and LVRR in patients with NICM.

Methods

We measured plasma miR-21 levels in 16 patients with NICM. LVRR was defined as increased LVEF by ≥10% and decreased LV end-diastolic diameter index by ≥10% from baseline data after optimal medication treatment at 1-year of follow-up. Further, we examined miR-21 expression and its potential role in cardiac fibrosis induced by transverse aortic constriction (TAC) in mice and angiotensin II (Ang II) stimulation in neonatal rat cardiomyocytes (NRCMs).

Results

There were 12 patients without LVRR and 4 patients with LVRR. Plasma miR-21 levels were significantly higher in patients without LVRR compared with those with LVRR. In TAC mice heart, miR-21 levels were significantly increased and programmed cell death 4 (PDCD4), a main target of miR-21, was decreased. In vitro, miR-21 levels were significantly increased and its upstream transcriptional factor, activator protein 1 (AP-1), was activated by Ang II stimulation in NRCMs. After transfection of miR-21 specific inhibitor, PDCD4 levels were upregulated. Furthermore, AP-1 activity, expression of collagen type I, and α-smooth muscle actin levels were significantly decreased after miR-21 inhibition.

Conclusions

These findings suggested that miR-21/PDCD4/AP-1 feedback loop pathway was involved in LVRR in patients with NICM by promoting cardiac fibrosis. MiR-21 can be the therapeutic target in NICM.

P5607Clinical characteristics and treatment strategy for acute aortic dissection in Tokyo Acute Aortic Disease Super-Network System

Introduction

Acute aortic dissection (AAD) is one of the most fatal cardiovascular diseases. The prevalence of AAD is reported to be low. The clinical data of AAD from representative cardiovascular centers are not enough to show the whole range of clinical feature of AAD. We have to know the exact prevalence and clinical pictures of AAD under the new system, the Tokyo AAD Super-Network System (TAAD-SNS), for strategy of emergency transport and treatment of AAD which would cover the entire metropolitan area of Tokyo. TAAD-SNS started in 2011, and after slight modification, the new system of AAD re-started in 2013. The aim of this study is to elucidate the whole range of clinical characteristics and recent trends of treatment of AAD.

Methods

Out of 73 hospitals included in Tokyo CCU Network system, 41 hospitals are chosen for TAAD-SNS. These hospitals provide around-the-clock surgery. In this system, the availability of surgical division is monitored in real time. All of the patients suspected of AAD are transferred directly or from primary care hospital to the hospitals of TAAD-SNS.

Results

After exclusion of 237 patients with cardiopulmonary arrest on arrival, 4877 consecutive patients (2923 male, mean age of 69±14 y/o) were admitted to the hospitals with diagnosis of AAD from 2013 to 2016. Prevalence of AAD in Tokyo was about 10 patients per 100,000 populations in every year. After exclusion of 37 patients undetermined into type A or B, 4840 patients (2694 with type A and 2146 with type B) were analyzed. Among the type A patients, 1752 (65%) were classified into type of patent false lumen (classic-type), 721 (27%) of closed false lumen (intramural hematoma: IMH-type), and 221 (8%) were undetermined. Among the type B, 880 (41%) were classified into classic-type, 1129 (53%) of IMH-type, and 137 (6%) were undetermined. Both among type A and B, mean ages were younger in classic-type than in IMH-type (type A: 66±14 vs. 73±12 y/o, p<0.05; type B: 64±15 vs. 72±12 y/o, p<0.05). Prevalence of male population and risk factor of hypertension was higher in type B than in type A both among classic-type and IMH-type. Systolic blood pressure at the emergency room was lower in type A than in type B among both classic-type and IMH-type (classic-type: 124±34 vs. 161±38 mmHg, IMH-type: 130±51 vs. 163±56 mmHg). In-hospital mortality of surgical treatment for type A classic-type and type A IMH-type, conservative strategy for type B classic-type and type B IMH-type was 9.6%, 4.2%, 3.1% and 1.7%, respectively. Stentgraft implantation for type B AAD started and shows a favorable in-hospital mortality compared to the operative treatment (Stentgraft vs. surgery in type B classic-type: 7.8% vs. 6.5%, in type B IMH-type: 10.7% vs. 11.8%, respectively).

Conclusion

Our study showed that prevalence of AAD was 2–3 times higher than previous reports. We should consider to choose the treatment strategy according to the type of AAD, A or B, classic-type or IMH-type.

Acknowledgement/Funding

Tokyo Metropolitan government

P1615HECT-Type Ubiquitin E3 Ligase ITCH attenuates cardiac hypertrophy by suppressing Wnt signaling pathway

Background

The homologous to the E6-AP carboxyl terminus (HECT)–type ubiquitin E3 ligase ITCH is an enzyme that plays an important role in ubiquitin proteasomal protein degradation. Dishevelled proteins (Dvl1, Dvl2 and Dvl3), which are involved in canonical Wnt/β catenin signaling pathway, play a role in cardiac hypertrophy.

Purpose

The aim of this study was to examine whether ITCH interacts with Dvls and prevents cardiac hypertrophy induced by pressure overload.

Methods and results

We confirmed the protein interaction between ITCH and Dvls in cardiomyocytes. Overexpression of ITCH decreased protein expression levels of Dvls, phospho-GSK3β and β-catenin. Conversely, knockdown of ITCH using small interfering RNA augmented canonical Wnt/β catenin signaling pathway. Thoracic transverse aortic constriction (TAC) was performed in transgenic mice with cardiac-specific overexpression of ITCH (ITCH-Tg) and wild-type (WT) mice. The canonical Wnt/β catenin signaling pathway was inhibited and cardiac hypertrophy was attenuated in ITCH-Tg mice compared with WT mice after TAC.

Overexpression of ITCH in cardiomyocytes

Conclusion

We demonstrated that ITCH targets Dvls for ubiquitin-proteasome degradation in cardiomyocytes and ameliorates cardiac hypertrophy by suppressing canonical Wnt/β catenin signaling pathway.

Energy Spectrum of Two-Dimensional Excitons in a Nonuniform Dielectric Medium

We demonstrate that, in monolayers (MLs) of semiconducting transition metal dichalcogenides, the s-type Rydberg series of excitonic states follows a simple energy ladder: ε_{n}=-Ry^{*}/(n+δ)^{2}, n=1,2,…, in which Ry^{*} is very close to the Rydberg energy scaled by the dielectric constant of the medium surrounding the ML and by the reduced effective electron-hole mass, whereas the ML polarizability is accounted for only by δ. This is justified by the analysis of experimental data on excitonic resonances, as extracted from magneto-optical measurements of a high-quality WSe_{2} ML encapsulated in hexagonal boron nitride (hBN), and well reproduced with an analytically solvable Schrödinger equation when approximating the electron-hole potential in the form of a modified Kratzer potential. Applying our convention to other MoSe_{2}, WS_{2}, MoS_{2} MLs encapsulated in hBN, we estimate an apparent magnitude of δ for each of the studied structures. Intriguingly, δ is found to be close to zero for WSe_{2} as well as for MoS_{2} monolayers, what implies that the energy ladder of excitonic states in these two-dimensional structures resembles that of Rydberg states of a three-dimensional hydrogen atom.

Probing and Manipulating Valley Coherence of Dark Excitons in Monolayer WSe_{2}

Monolayers of semiconducting transition metal dichalcogenides are two-dimensional direct-gap systems which host tightly bound excitons with an internal degree of freedom corresponding to the valley of the constituting carriers. Strong spin-orbit interaction and the resulting ordering of the spin-split subbands in the valence and conduction bands makes the lowest-lying excitons in WX_{2} (X being S or Se) spin forbidden and optically dark. With polarization-resolved photoluminescence experiments performed on a WSe_{2} monolayer encapsulated in a hexagonal boron nitride, we show how the intrinsic exchange interaction in combination with the applied in-plane and/or out-of-plane magnetic fields enables one to probe and manipulate the valley degree of freedom of the dark excitons.

Interaction-Induced Shubnikov-de Haas Oscillations in Optical Conductivity of Monolayer MoSe_{2}

We report polarization-resolved resonant reflection spectroscopy of a charge-tunable atomically thin valley semiconductor hosting tightly bound excitons coupled to a dilute system of fully spin- and valley-polarized holes in the presence of a strong magnetic field. We find that exciton-hole interactions manifest themselves in hole-density dependent, Shubnikov-de Haas-like oscillations in the energy and line broadening of the excitonic resonances. These oscillations are evidenced to be precisely correlated with the occupation of Landau levels, thus demonstrating that strong interactions between the excitons and Landau-quantized itinerant carriers enable optical investigation of quantum-Hall physics in transition metal dichalcogenides.

Control of the Exciton Radiative Lifetime in van der Waals Heterostructures

Optical properties of atomically thin transition metal dichalcogenides are controlled by robust excitons characterized by a very large oscillator strengths. Encapsulation of monolayers such as MoSe_{2} in hexagonal boron nitride (hBN) yields narrow optical transitions approaching the homogenous exciton linewidth. We demonstrate that the exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect. The time-resolved photoluminescence measurements show that the neutral exciton spontaneous emission time can be tuned by one order of magnitude depending on the thickness of the surrounding hBN layers. The inhibition of the radiative recombination can yield spontaneous emission time up to 10 ps. These results are in very good agreement with the calculated recombination rate in the weak exciton-photon coupling regime. The analysis shows that we are also able to observe a sizable enhancement of the exciton radiative decay rate. Understanding the role of these electrodynamical effects allows us to elucidate the complex dynamics of relaxation and recombination for both neutral and charged excitons.