Highly tunable ground and excited state excitonic dipoles in multilayer 2H-MoSe2.

The fundamental properties of an exciton are determined by the spin, valley, energy, and spatial wavefunctions of the Coulomb-bound electron and hole. In van der Waals materials, these attributes can be widely engineered through layer stacking configuration to create highly tunable interlayer excitons with static out-of-plane electric dipoles, at the expense of the strength of the oscillating in-plane dipole responsible for light-matter coupling. Here we show that interlayer excitons in bi- and tri-layer 2H-MoSe2 crystals exhibit electric-field-driven coupling with the ground (1s) and excited states (2s) of the intralayer A excitons. We demonstrate that the hybrid states of these distinct exciton species provide strong oscillator strength, large permanent dipoles (up to 0.73 ± 0.01 enm), high energy tunability (up to ~200 meV), and full control of the spin and valley characteristics such that the exciton g-factor can be manipulated over a large range (from -4 to +14). Further, we observe the bi- and tri-layer excited state (2s) interlayer excitons and their coupling with the intralayer excitons states (1s and 2s). Our results, in good agreement with a coupled oscillator model with spin (layer)-selectivity and beyond standard density functional theory calculations, promote multilayer 2H-MoSe2 as a highly tunable platform to explore exciton-exciton interactions with strong light-matter interactions.

Disposition of emergency department patients with acute pulmonary embolism after ambulance arrival.

Objective: Most outpatients with pulmonary embolism (PE) are diagnosed in the emergency department (ED). The relationship between means of arrival, site of diagnosis, and disposition in ED patients with PE is unknown. We compared discharge home between patients arriving by emergency medical services (EMS) and those arriving by other means. Within the EMS cohort, we compared those with a recent PE diagnosis in the outpatient clinic setting to those who were diagnosed with PE in the ED. Methods: This study was a secondary analysis of a retrospective cohort that included all adult, non-pregnant ED patients treated for acute PE across 21 community EDs from January 2013 to April 2015. The primary outcome was discharge home within 24 h of ED registration; we also examined mortality. We described associations with patient arrival method and other patient characteristics. Results: Among 2996 ED patient encounters with acute PE, 644 (21.5%) arrived by EMS. This group had a lower frequency of discharge (9.2% vs 26.4%) and higher 30-day all-cause mortality (8.7% vs 3.1%) than their counterparts (p < 0.001 for both). These associations remained after adjusting for confounding variables. Among the EMS cohort, 14 patients (2.2%) arrived with a PE diagnosis recently made in the outpatient setting. Conclusion: Patients with PE who arrived at the ED by EMS were less likely to be discharged home within 24 h and more likely to die within 30 days than those who arrived by other means. Less than 3% of the EMS group had been diagnosed with PE before ED arrival.

Effort feels meaningful.

People often dislike effort and avoid it when they can, but effort can also imbue tasks with meaning. This is the case for real-life tasks, but also novel tasks devoid of true purpose. Why does effort feel meaningful, under what conditions, and for whom?

Optical read-out of Coulomb staircases in a moiré superlattice via trapped interlayer trions.

Moiré patterns with a superlattice potential can be formed by vertically stacking two layered materials with a relative twist or lattice constant mismatch. In transition metal dichalcogenide-based systems, the moiré potential landscape can trap interlayer excitons (IXs) at specific atomic registries. Here, we report that spatially isolated trapped IXs in a molybdenum diselenide/tungsten diselenide heterobilayer device provide a sensitive optical probe of carrier filling in their immediate environment. By mapping the spatial positions of individual trapped IXs, we are able to spectrally track the emitters as the moiré lattice is filled with excess carriers. Upon initial doping of the heterobilayer, neutral trapped IXs form charged IXs (IX trions) uniformly with a binding energy of ~7 meV. Upon further doping, the empty superlattice sites sequentially fill, creating a Coulomb staircase: stepwise changes in the IX trion emission energy due to Coulomb interactions with carriers at nearest-neighbour moiré sites. This non-invasive, highly local technique can complement transport and non-local optical sensing techniques to characterize Coulomb interaction energies, visualize charge correlated states, or probe local disorder in a moiré superlattice.

Spin-layer locking of interlayer excitons trapped in moiré potentials.

Van der Waals heterostructures offer attractive opportunities to design quantum materials. For instance, transition metal dichalcogenides (TMDs) possess three quantum degrees of freedom: spin, valley index and layer index. Furthermore, twisted TMD heterobilayers can form moiré patterns that modulate the electronic band structure according to the atomic registry, leading to spatial confinement of interlayer excitons (IXs). Here we report the observation of spin-layer locking of IXs trapped in moiré potentials formed in a heterostructure of bilayer 2H-MoSe2 and monolayer WSe2. The phenomenon of locked electron spin and layer index leads to two quantum-confined IX species with distinct spin-layer-valley configurations. Furthermore, we observe that the atomic registries of the moiré trapping sites in the three layers are intrinsically locked together due to the 2H-type stacking characteristic of bilayer TMDs. These results identify the layer index as a useful degree of freedom to engineer tunable few-level quantum systems in two-dimensional heterostructures.