Orthorhombic lead-free hybrid perovskite CHNHSnI under strain: an study.

We report a computational study where we explore the possibility of tuning the electronic properties of orthorhombic methylammonium tin iodide CHNHSnI using strains. According to our findings, a moderate [001] strain, smaller than 2%, would open the band gap up to 1.25 eV and enhance the exciton binding energy, opening up new possibilities for the use of CHNHSnI in technological applications.

Strong Coupling of Coherent Phonons to Excitons in Semiconducting Monolayer MoTe.

The coupling of the electron system to lattice vibrations and their time-dependent control and detection provide unique insight into the nonequilibrium physics of semiconductors. Here, we investigate the ultrafast transient response of semiconducting monolayer 2-MoTe encapsulated with BN using broadband optical pump-probe microscopy. The sub-40 fs pump pulse triggers extremely intense and long-lived coherent oscillations in the spectral region of the A' and B' exciton resonances, up to ∼20% of the maximum transient signal, due to the displacive excitation of the out-of-plane phonon.

Inhomogeneous Broadening of Photoluminescence Spectra and Kinetics of Nanometer-Thick (Phenethylammonium)PbI Perovskite Thin Films: Implications for Optoelectronics.

An outstanding potentiality of layered two-dimensional (2D) organic-inorganic hybrid perovskites (2DHPs) is in the development of solar cells, photodetectors, and light-emitting diodes. In 2DHPs, an exciton is localized in an atomically thin lead(II) halide inorganic layer of sub-nanometer thickness as in a quantum well sandwiched between organic layers as energetic and dielectric barriers. In previous years, versatile optical characterization of 2DHPs has been carried out mainly for thin flakes of single crystals and ultrathin (of the order of 20 nm) polycrystalline films, whereas there is a lack of optical characterization of thick (hundreds of nanometers) polycrystalline films, fundamentals for fabrication of devices.

Time-Dependent Screening Explains the Ultrafast Excitonic Signal Rise in 2D Semiconductors.

We calculate the time evolution of the transient reflection signal in an MoS monolayer on a SiO/Si substrate using first-principles out-of-equilibrium real-time methods. Our simulations provide a simple and intuitive physical picture for the delayed, yet ultrafast, evolution of the signal whose rise time depends on the excess energy of the pump laser: at laser energies above the A- and B-exciton, the pump pulse excites electrons and holes far away from the K valleys in the first Brillouin zone. Electron-phonon and hole-phonon scattering lead to a gradual relaxation of the carriers toward small around K, enhancing the dielectric screening.

Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe/CrBr van der Waals heterostructures.

Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe and CrBr in photoluminescence, whereby the valley polarization of the MoSe trion state conforms closely to the local CrBr magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes.

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).

Strongly Coupled Coherent Phonons in Single-Layer MoS.

We present a transient absorption setup combining broadband detection over the visible-UV range with high temporal resolution (∼20 fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single-layer (1L)-MoS, as a representative semiconducting 1L-transition metal dichalcogenide (TMD), where the confined dynamical interaction between excitons and phonons is unexplored. The coherent oscillatory motion of the out-of-plane A' phonons, triggered by the ultrashort laser pulses, dynamically modulates the excitonic resonances on a time scale of few tens of fs.

Out-of-plane orientation of luminescent excitons in two-dimensional indium selenide.

Van der Waals materials offer a wide range of atomic layers with unique properties that can be easily combined to engineer novel electronic and photonic devices. A missing ingredient of the van der Waals platform is a two-dimensional crystal with naturally occurring out-of-plane luminescent dipole orientation. Here we measure the far-field photoluminescence intensity distribution of bulk InSe and two-dimensional InSe, WSe and MoSe.

Optical Contrast and Raman Spectroscopy Techniques Applied to Few-Layer 2D Hexagonal Boron Nitride.

The successful integration of few-layer thick hexagonal boron nitride (hBN) into devices based on two-dimensional materials requires fast and non-destructive techniques to quantify their thickness. Optical contrast methods and Raman spectroscopy have been widely used to estimate the thickness of two-dimensional semiconductors and semi-metals. However, they have so far not been applied to two-dimensional insulators.

Exciton-Phonon Coupling in the Ultraviolet Absorption and Emission Spectra of Bulk Hexagonal Boron Nitride.

We present an ab initio method to calculate phonon-assisted absorption and emission spectra in the presence of strong excitonic effects. We apply the method to bulk hexagonal BN, which has an indirect band gap and is known for its strong luminescence in the UV range. We first analyze the excitons at the wave vector q[over ¯] of the indirect gap.

Many-body perturbation theory calculations using the yambo code.

yambo is an open source project aimed at studying excited state properties of condensed matter systems from first principles using many-body methods. As input, yambo requires ground state electronic structure data as computed by density functional theory codes such as Quantum ESPRESSO and Abinit. yambo's capabilities include the calculation of linear response quantities (both independent-particle and including electron-hole interactions), quasi-particle corrections based on the GW formalism, optical absorption, and other spectroscopic quantities.

Intravalley Spin-Flip Relaxation Dynamics in Single-Layer WS.

In monolayer (1L) transition metal dichalcogenides (TMDs) the valence and conduction bands are spin-split because of the strong spin-orbit interaction. In tungsten-based TMDs the spin-ordering of the conduction band is such that the so-called dark excitons, consisting of electrons and holes with opposite spin orientation, have lower energy than A excitons. The transition from bright to dark excitons involves the scattering of electrons from the upper to the lower conduction band at the K point of the Brillouin zone, with detrimental effects for the optoelectronic response of 1L-TMDs, since this reduces their light emission efficiency.

[Pheochromocytoma giant cystic: a case report].

The giant cystic pheochromocytoma is a rare adrenal tumor in the predominantly asymptomatic course; so many cases are not diagnosed until the time of surgery. The simple mobilization of the tumor is associated with the passage to the blood of large amounts of catecholamines and high morbidity and mortality. So the surgery itself and perioperative management are a huge challenge.

Ab Initio Calculations of Ultrashort Carrier Dynamics in Two-Dimensional Materials: Valley Depolarization in Single-Layer WSe.

In single-layer WSe, a paradigmatic semiconducting transition metal dichalcogenide, a circularly polarized laser field can selectively excite electronic transitions in one of the inequivalent K valleys. Such selective valley population corresponds to a pseudospin polarization. This can be used as a degree of freedom in a "valleytronic" device provided that the time scale for its depolarization is sufficiently large.

Fermi energy dependence of the optical emission in core/shell InAs nanowire homostructures.

InAs nanowires grown by vapor-liquid-solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by ∼20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy.

Quantum Interference Effects in Resonant Raman Spectroscopy of Single- and Triple-Layer MoTe from First-Principles.

We present a combined experimental and theoretical study of resonant Raman spectroscopy in single- and triple-layer MoTe. Raman intensities are computed entirely from first-principles by calculating finite differences of the dielectric susceptibility. In our analysis, we investigate the role of quantum interference effects and the electron-phonon coupling.

Unified Description of the Optical Phonon Modes in N-Layer MoTe2.

N-layer transition metal dichalcogenides provide a unique platform to investigate the evolution of the physical properties between the bulk (three-dimensional) and monolayer (quasi-two-dimensional) limits. Here, using high-resolution micro-Raman spectroscopy, we report a unified experimental description of the Γ-point optical phonons in N-layer 2H-molybdenum ditelluride (MoTe2). We observe series of N-dependent low-frequency interlayer shear and breathing modes (below 40 cm(-1), denoted LSM and LBM) and well-defined Davydov splittings of the mid-frequency modes (in the range 100-200 cm(-1), denoted iX and oX), which solely involve displacements of the chalcogen atoms.

Probing quantum confinement within single core-multishell nanowires.

Theoretically core-multishell nanowires under a cross-section of hexagonal geometry should exhibit peculiar confinement effects. Using a hard X-ray nanobeam, here we show experimental evidence for carrier localization phenomena at the hexagon corners by combining synchrotron excited optical luminescence with simultaneous X-ray fluorescence spectroscopy. Applied to single coaxial n-GaN/InGaN multiquantum-well/p-GaN nanowires, our experiment narrows the gap between optical microscopy and high-resolution X-ray imaging and calls for further studies on the underlying mechanisms of optoelectronic nanodevices.

Anisotropic optical response of GaN and AlN nanowires.

We present a theoretical study of the electronic structure and optical properties of free-standing GaN and AlN nanowires. We have implemented the empirical tight-binding method, with an orbital basis sp(3), that includes the spin-orbit interaction. The passivation of the dangling bonds at the free surfaces is also studied, together with the effects on the electronic structure of the nanowire.

[Incidence of inflammatory bowel disease in the health area of Navalmoral de la Mata (Caceres, Spain) between 2000 and 2009].

Objectives: To determine whether the incidence of inflammatory bowel disease (IBD) has changed in our area and whether it has been influenced by the growing immigrant population.

Population And Methods: From 2000 to 2009, a prospective population-based study was conducted in the population aged over 15 years old and was compared with a study carried out from 1994 to 1998 in the health area of Campo Arañuelo. The distribution of Crohn's disease (CD), ulcerative colitis (UC) and age and sex were analyzed and compared with European rates for the standard population, both for the total population and for the local population.

[Lipoma of the stomach. Presentation of a case and a review of cases reported in Spain].

Gastric lipoma is an infrequent benign submucosal tumor that is usually asymptomatic. In view of the few reports of this pathology in the Spanish and international bibliography, a new case that debuted as massive upper gastrointestinal hemorrhage is communicated. We reviewed the cases published in Spain to date, emphasizing the methodology of preoperative diagnosis, with special attention to the endoscopic signs characterizing gastric lipoma and computerized axial tomography, which is now viewed as the technique of choice.

[Lactic acidosis in recovered asphyctic newborn infants].

Thirty newborn babies delivered by elective caesarean section were studied. They were randomly placed in two groups. The first group consisted of newborns who scored 3 or less on the Apgar scale at one minute and 8 or more after five minutes.