Lightwave valleytronics in a monolayer of tungsten diselenide.

As conventional electronics approaches its limits 1 , nanoscience has urgently sought methods of fast control of electrons at the fundamental quantum level 2 . Lightwave electronics 3 -the foundation of attosecond science 4 -uses the oscillating carrier wave of intense light pulses to control the translational motion of the electron's charge faster than a single cycle of light5-15. Despite being particularly promising information carriers, the internal quantum attributes of spin 16 and valley pseudospin17-21 have not been switchable on the subcycle scale. Here we demonstrate lightwave-driven changes of the valley pseudospin and introduce distinct signatures in the optical readout. Photogenerated electron-hole pairs in a monolayer of tungsten diselenide are accelerated and collided by a strong lightwave. The emergence of high-odd-order sidebands and anomalous changes in their polarization direction directly attest to the ultrafast pseudospin dynamics. Quantitative computations combining density functional theory with a non-perturbative quantum many-body approach assign the polarization of the sidebands to a lightwave-induced change of the valley pseudospin and confirm that the process is coherent and adiabatic. Our work opens the door to systematic valleytronic logic at optical clock rates.

Lightwave-driven quasiparticle collisions on a subcycle timescale.

Ever since Ernest Rutherford scattered α-particles from gold foils, collision experiments have revealed insights into atoms, nuclei and elementary particles. In solids, many-body correlations lead to characteristic resonances--called quasiparticles--such as excitons, dropletons, polarons and Cooper pairs. The structure and dynamics of quasiparticles are important because they define macroscopic phenomena such as Mott insulating states, spontaneous spin- and charge-order, and high-temperature superconductivity. However, the extremely short lifetimes of these entities make practical implementations of a suitable collider challenging. Here we exploit lightwave-driven charge transport, the foundation of attosecond science, to explore ultrafast quasiparticle collisions directly in the time domain: a femtosecond optical pulse creates excitonic electron-hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying dynamics of the wave packets, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands of the optical excitation. A full quantum theory explains our observations microscopically. This approach enables collision experiments with various complex quasiparticles and suggests a promising new way of generating sub-femtosecond pulses.

Ultrafast transition between exciton phases in van der Waals heterostructures.

Heterostructures of atomically thin van der Waals bonded monolayers have opened a unique platform to engineer Coulomb correlations, shaping excitonic1-3, Mott insulating4 or superconducting phases5,6. In transition metal dichalcogenide heterostructures7, electrons and holes residing in different monolayers can bind into spatially indirect excitons1,3,8-11 with a strong potential for optoelectronics11,12, valleytronics1,3,13, Bose condensation14, superfluidity14,15 and moiré-induced nanodot lattices16. Yet these ideas require a microscopic understanding of the formation, dissociation and thermalization dynamics of correlations including ultrafast phase transitions. Here we introduce a direct ultrafast access to Coulomb correlations between monolayers, where phase-locked mid-infrared pulses allow us to measure the binding energy of interlayer excitons in WSe2/WS2 hetero-bilayers by revealing a novel 1s-2p resonance, explained by a fully quantum mechanical model. Furthermore, we trace, with subcycle time resolution, the transformation of an exciton gas photogenerated in the WSe2 layer directly into interlayer excitons. Depending on the stacking angle, intra- and interlayer species coexist on picosecond scales and the 1s-2p resonance becomes renormalized. Our work provides a direct measurement of the binding energy of interlayer excitons and opens the possibility to trace and control correlations in novel artificial materials.

Resonant internal quantum transitions and femtosecond radiative decay of excitons in monolayer WSe2.

Atomically thin two-dimensional crystals have revolutionized materials science. In particular, monolayer transition metal dichalcogenides promise novel optoelectronic applications, owing to their direct energy gaps in the optical range. Their electronic and optical properties are dominated by Coulomb-bound electron-hole pairs called excitons, whose unusual internal structure, symmetry, many-body effects and dynamics have been vividly discussed. Here we report the first direct experimental access to all 1s A excitons, regardless of momentum--inside and outside the radiative cone--in single-layer WSe2. Phase-locked mid-infrared pulses reveal the internal orbital 1s-2p resonance, which is highly sensitive to the shape of the excitonic envelope functions and provides accurate transition energies, oscillator strengths, densities and linewidths. Remarkably, the observed decay dynamics indicates an ultrafast radiative annihilation of small-momentum excitons within 150 fs, whereas Auger recombination prevails for optically dark states. The results provide a comprehensive view of excitons and introduce a new degree of freedom for quantum control, optoelectronics and valleytronics of dichalcogenide monolayers.

On possible involvement of adrenocorticoids in chicken spleen development.

The possible effects of glucocorticoids on spleen development were assessed by the determination of changes in mean organ weight and histology in chicken (Gallus gallus) embryos at stages 44 and 45 of Hamburger and Hamilton on days 19.5 and 20 of incubation (N = 10--13). After the administration of 1 to 6 mg of metopirone (an 11-beta-hydroxylase inhibitor) the numbers of white-pulp periarterial nests and red-pulp granulocytes decreased. The changes associated with metopirone treatment were less evident after the addition of corticosterone (20 and 200 microgram). After adding corticosterone alone (200 microgram), the white-pulp nests appeared larger than in control. Mean body and spleen weights or spleen-body weight ratios did not change much after treatment. Possibly glucocorticoids normally direct these aspects of spleen histogenesis in chicken embryos.

The concentration of bupivacaine in fetal organs during obstetrical epidural analgesia.

The concentration of bupivacaine in organs of non-viable human fetuses after obstetrical epidural analgesia in customary doses was investigated. The concentrations were determined with a gas chromatograph. The material consisted of a fetus who died following termination in the 24th week of pregnancy three minutes after birth without spontaneous respiration. The other fetus was born maturely in the 40th pregnancy week with anencephaly who lived 20 minutes following initial spontaneous respiration. Most noteworthy were the increased concentrations in the liver indicating the important metabolic function of the liver for the metabolism of bupivacaine in the fetus. Further a very high pulmonary concentration was found in the mature fetus. Even though blood gases analysis were not performed we conclude that: the lung is the best perfused organ after birth and onset of spontaneous respiration because of the closure of the ductus arteriosus; because of the increasing agonal respiratory acidosis, bupivacaine accumulates in the lung, the organ from which the acidosis originates. Also, the ionized form the bupivacaine is unable to leave the intracellular space. For the clinical use of epidural analgesia during delivery, these results constitute an important indication for avoiding fetal acidosis before and during the action of such analgesia. This mandates strict and continuous fetal monitoring. Our results in agreement with other authors show that during fetal acidosis and simultaneous administration of bupivacaine the fetal distress may be potentiated by an accelerated transfer of the anesthetic agent into the fetal placental space. Under normal conditions one may assume that this technique of analgesia has a positive effect on the fetus because of the improved placental perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

[Bacterial sacroiliitis]. / Bakterielle Sakroiliitis.

We saw two cases of infectious sacroiliitis in young patients. The multi-various clinical symptoms, the predispositions, as well as the alteration of laboratory analyses are described. Further, we discuss problems of early diagnosis, diagnostic measures like x-ray, sonography, bone-scan, computerized tomography scan, magnetic resonance imaging, and their particular significance. Computerized tomography scan of iliosacral joints determined the further therapeutic procedure. In both cases, we prescribed cephalosporin-antibiotic cefotaxime-sodium.