Control of the Bright-Dark Exciton Splitting Using the Lamb Shift in a Two-Dimensional Semiconductor.

We investigate the exciton fine structure in atomically thin WSe_{2}-based van der Waals heterostructures where the density of optical modes at the location of the semiconductor monolayer can be tuned. The energy splitting Δ between the bright and dark exciton is measured by photoluminescence spectroscopy. We demonstrate that Δ can be tuned by a few meV as a result of a significant Lamb shift of the optically active exciton that arises from emission and absorption of virtual photons triggered by the vacuum fluctuations of the electromagnetic field.

Spin/valley pumping of resident electrons in WSe and WS monolayers.

Monolayers of transition metal dichalcogenides are ideal materials to control both spin and valley degrees of freedom either electrically or optically. Nevertheless, optical excitation mostly generates excitons species with inherently short lifetime and spin/valley relaxation time. Here we demonstrate a very efficient spin/valley optical pumping of resident electrons in n-doped WSe and WS monolayers.

Optical properties of excitons in two-dimensional transition metal dichalcogenide nanobubbles.

Strain in two-dimensional transition metal dichalcogenide has led to localized states with exciting optical properties, in particular, in view of designing one photon sources. The naturally formed nanobubbles when the MoS monolayer is deposited on an hBN substrate lead to a local reduction in the band gap due to strain developing in the nanobubble. The photogenerated particles are thus confined in the strain-induced potential.

Measurement of Conduction and Valence Bands g-Factors in a Transition Metal Dichalcogenide Monolayer.

The electron valley and spin degree of freedom in monolayer transition-metal dichalcogenides can be manipulated in optical and transport measurements performed in magnetic fields. The key parameter for determining the Zeeman splitting, namely, the separate contribution of the electron and hole g factor, is inaccessible in most measurements. Here we present an original method that gives access to the respective contribution of the conduction and valence band to the measured Zeeman splitting.

Measurement of the spin-forbidden dark excitons in MoS and MoSe 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 MoS and MoSe monolayers encapsulated in boron nitride by magneto-photoluminescence spectroscopy in magnetic fields up to 30 T.

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.

Extracorporeal CO removal and regional citrate anticoagulation in an experimental model of hypercapnic acidosis.

Low flow extracorporeal veno-venous CO removal (ECCO R) therapy is used to remove CO while reducing ventilation intensity. However, the use of this technique is limited because efficiency of CO removal and potential beneficial effects on pulmonary hemodynamics are not precisely established. Moreover, this technique requires anticoagulation that may induce severe complications in critically ill patients.

Electrical Initialization of Electron and Nuclear Spins in a Single Quantum Dot at Zero Magnetic Field.

The emission of circularly polarized light from a single quantum dot relies on the injection of carriers with well-defined spin polarization. Here we demonstrate single dot electroluminescence (EL) with a circular polarization degree up to 35% at zero applied magnetic field. The injection of spin-polarized electrons is achieved by combining ultrathin CoFeB electrodes on top of a spin-LED device with p-type InGaAs quantum dots in the active region.

In-Plane Propagation of Light in Transition Metal Dichalcogenide Monolayers: Optical Selection Rules.

The optical selection rules for interband transitions in WSe_{2}, WS_{2}, and MoSe_{2} transition metal dichalcogenide monolayers are investigated by polarization-resolved photoluminescence experiments with a signal collection from the sample edge. These measurements reveal a strong polarization dependence of the emission lines. We see clear signatures of the emitted light with the electric field oriented perpendicular to the monolayer plane, corresponding to an interband optical transition forbidden at normal incidence used in standard optical spectroscopy measurements.

Enabling valley selective exciton scattering in monolayer WSe through upconversion.

Excitons, Coulomb bound electron-hole pairs, are composite bosons and their interactions in traditional semiconductors lead to condensation and light amplification. The much stronger Coulomb interaction in transition metal dichalcogenides such as WSe monolayers combined with the presence of the valley degree of freedom is expected to provide new opportunities for controlling excitonic effects. But so far the bosonic character of exciton scattering processes remains largely unexplored in these two-dimensional materials.

Control of Exciton Valley Coherence in Transition Metal Dichalcogenide Monolayers.

The direct gap interband transitions in transition metal dichalcogenide monolayers are governed by chiral optical selection rules. Determined by laser helicity, optical transitions in either the K^{+} or K^{-} valley in momentum space are induced. Linearly polarized laser excitation prepares a coherent superposition of valley states.

Spin-orbit engineering in transition metal dichalcogenide alloy monolayers.

Binary transition metal dichalcogenide monolayers share common properties such as a direct optical bandgap, spin-orbit splittings of hundreds of meV, light-matter interaction dominated by robust excitons and coupled spin-valley states. Here we demonstrate spin-orbit-engineering in Mo(1-x)WxSe2 alloy monolayers for optoelectronics and applications based on spin- and valley-control. We probe the impact of the tuning of the conduction band spin-orbit spin-splitting on the bright versus dark exciton population.

Double resonant Raman scattering and valley coherence generation in monolayer WSe_{2}.

The electronic states at the direct band gap of monolayer transition metal dichalcogenides such as WSe_{2} at the K^{+} and K^{-} valleys are related by time reversal and may be viewed as pseudospins. The corresponding optical interband transitions are governed by robust excitons. Excitation with linearly polarized light yields the coherent superposition of exciton pseudospin states, referred to as coherent valley states.

Giant enhancement of the optical second-harmonic emission of WSe(2) monolayers by laser excitation at exciton resonances.

We show that the light-matter interaction in monolayer WSe_{2} is strongly enhanced when the incoming electromagnetic wave is in resonance with the energy of the exciton states of strongly Coulomb bound electron-hole pairs below the electronic band gap. We perform second harmonic generation (SHG) spectroscopy as a function of laser energy and polarization at T=4  K. At the exciton resonance energies we record an enhancement by up to 3 orders of magnitude of the SHG efficiency, due to the unusual combination of electric dipole and magnetic dipole transitions.

Use of a pediatric oxygenator integrated in a veno-venous hemofiltration circuit to remove CO2: a case report in a severe burn patient with refractory hypercapnia.

Acute respiratory distress syndrome management is currently based on lung protective ventilation. Such strategy may lead to hypercapnic acidosis. We report a case of refractory hypercapnia in a severe burn adult, treated with simplified veno-venous extracorporeal carbon dioxide removal technique.

Carrier and polarization dynamics in monolayer MoS2.

In monolayer MoS2, optical transitions across the direct band gap are governed by chiral selection rules, allowing optical valley initialization. In time-resolved photoluminescence (PL) experiments, we find that both the polarization and emission dynamics do not change from 4 to 300 K within our time resolution. We measure a high polarization and show that under pulsed excitation the emission polarization significantly decreases with increasing laser power.

Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field.

Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots.

Low-temperature photoluminescence study of exciton recombination in bulk GaAsBi.

The exciton recombination processes in a series of elastically strained GaAsBi epilayers are investigated by means of time-integrated and time-resolved photoluminescence at T = 10 K. The bismuth content in the samples was adjusted from 1.16% to 3.

Gate control of the electron spin-diffusion length in semiconductor quantum wells.

The spin diffusion length is a key parameter to describe the transport properties of spin polarized electrons in solids. Electrical spin injection in semiconductor structures, a major issue in spintronics, critically depends on this spin diffusion length. Gate control of the spin diffusion length could be of great importance for the operation of devices based on the electric field manipulation and transport of electron spin.

Dark-bright mixing of interband transitions in symmetric semiconductor quantum dots.

In photoluminescence spectra of symmetric [111] grown GaAs/AlGaAs quantum dots in longitudinal magnetic fields applied along the growth axis, we observe in addition to the expected bright states also nominally dark transitions for both charged and neutral excitons. We uncover a strongly nonmonotonic, sign-changing field dependence of the bright neutral exciton splitting resulting from the interplay between exchange and Zeeman effects. Our theory shows quantitatively that these surprising experimental results are due to magnetic-field-induced ±3/2 heavy-hole mixing, an inherent property of systems with C(3v) point-group symmetry.

Full electrical control of the electron spin relaxation in GaAs quantum wells.

The electron spin dynamics in (111)-oriented GaAs/AlGaAs quantum wells is studied by time-resolved photoluminescence spectroscopy. By applying an external electric field of 50 kV/cm a two-order of magnitude increase of the spin relaxation time can be observed reaching values larger than 30 ns; this is a consequence of the electric field tuning of the spin-orbit conduction band splitting which can almost vanish when the Rashba term compensates exactly the Dresselhaus one. The measurements under a transverse magnetic field demonstrate that the electron spin relaxation time for the three space directions can be tuned simultaneously with the applied electric field.

Robust quantum dot exciton generation via adiabatic passage with frequency-swept optical pulses.

The energy states in semiconductor quantum dots are discrete as in atoms, and quantum states can be coherently controlled with resonant laser pulses. Long coherence times allow the observation of Rabi flopping of a single dipole transition in a solid state device, for which occupancy of the upper state depends sensitively on the dipole moment and the excitation laser power. We report on the robust population inversion in a single quantum dot using an optical technique that exploits rapid adiabatic passage from the ground to an excited state through excitation with laser pulses whose frequency is swept through the resonance.

Anomalous Hanle effect due to optically created transverse overhauser field in single InAs/GaAs quantum dots.

We report on experimental observations of an anomalous Hanle effect in individual self-assembled InAs/GaAs quantum dots. A sizable electron spin polarization photocreated under constant illumination is maintained in transverse magnetic fields as high as approximately 1 T, up to a critical field where it abruptly collapses. These striking anomalies of the Hanle curve point to a novel mechanism of dynamic nuclear spin polarization giving rise to an effective magnetic field generated perpendicular to the optically injected electron spin polarization.

The Murine Angiotensin II-Induced Abdominal Aortic Aneurysm Model: Rupture Risk and Inflammatory Progression Patterns.

An abdominal aortic aneurysm (AAA) is an enlargement of the greatest artery in the body defined as an increase in diameter of 1.5-fold. AAAs are common in the elderly population and thousands die each year from their complications.

Controlling the polarization eigenstate of a quantum dot exciton with light.

We demonstrate optical control of the polarization eigenstates of a neutral quantum dot exciton without any external fields. By varying the excitation power of a circularly polarized laser in microphotoluminescence experiments on individual InGaAs quantum dots we control the magnitude and direction of an effective internal magnetic field created via optical pumping of nuclear spins. The adjustable nuclear magnetic field allows us to tune the linear and circular polarization degree of the neutral exciton emission.