The squeezed dark nuclear spin state in lead halide perovskites.

Coherent many-body states are highly promising for robust quantum information processing. While far-reaching theoretical predictions have been made for various implementations, direct experimental evidence of their appealing properties can be challenging. Here, we demonstrate optical manipulation of the nuclear spin ensemble in the lead halide perovskite semiconductor FAPbBr3 (FA = formamidinium), targeting a long-postulated collective dark state that is insensitive to optical pumping after its build-up. Via optical orientation of localized hole spins we drive the nuclear many-body system into this entangled state, requiring a weak magnetic field of only a few milli-Tesla strength at cryogenic temperatures. During its fast establishment, the nuclear polarization along the optical axis remains small, while the transverse nuclear spin fluctuations are strongly reduced, corresponding to spin squeezing as evidenced by a strong violation of the generalized nuclear squeezing-inequality with ξs < 0.5. The dark state corresponds to an ~35-body entanglement between the nuclei. Dark nuclear spin states can be exploited to store quantum information benefiting from their long-lived many-body coherence and to perform quantum measurements with a precision beyond the standard limit.

Mode locking of hole spin coherences in CsPb(Cl, Br)3 perovskite nanocrystals.

The spin physics of perovskite nanocrystals with confined electrons or holes is attracting increasing attention, both for fundamental studies and spintronic applications. Here, stable [Formula: see text] lead halide perovskite nanocrystals embedded in a fluorophosphate glass matrix are studied by time-resolved optical spectroscopy to unravel the coherent spin dynamics of holes and their interaction with nuclear spins of the 207Pb isotope. We demonstrate the spin mode locking effect provided by the synchronization of the Larmor precession of single hole spins in each nanocrystal in the ensemble that are excited periodically by a laser in an external magnetic field. The mode locking is enhanced by nuclei-induced frequency focusing. An ensemble spin dephasing time [Formula: see text] of a nanosecond and a single hole spin coherence time of T2 = 13 ns are measured. The developed theoretical model accounting for the mode locking and nuclear focusing for randomly oriented nanocrystals with perovskite band structure describes the experimental data very well.

The Landé factors of electrons and holes in lead halide perovskites: universal dependence on the band gap.

The Landé or g-factors of charge carriers are decisive for the spin-dependent phenomena in solids and provide also information about the underlying electronic band structure. We present a comprehensive set of experimental data for values and anisotropies of the electron and hole Landé factors in hybrid organic-inorganic (MAPbI3, MAPb(Br0.5Cl0.5)3, MAPb(Br0.05Cl0.95)3, FAPbBr3, FA0.9Cs0.1PbI2.8Br0.2, MA=methylammonium and FA=formamidinium) and all-inorganic (CsPbBr3) lead halide perovskites, determined by pump-probe Kerr rotation and spin-flip Raman scattering in magnetic fields up to 10 T at cryogenic temperatures. Further, we use first-principles density functional theory (DFT) calculations in combination with tight-binding and k ⋅ p approaches to calculate microscopically the Landé factors. The results demonstrate their universal dependence on the band gap energy across the different perovskite material classes, which can be summarized in a universal semi-phenomenological expression, in good agreement with experiment.

Low voltage control of exchange coupling in a ferromagnet-semiconductor quantum well hybrid structure.

Voltage control of ferromagnetism on the nanometer scale is highly appealing for the development of novel electronic devices with low power consumption, high operation speed, reliable reversibility and compatibility with semiconductor technology. Hybrid structures based on the assembly of ferromagnetic and semiconducting building blocks are expected to show magnetic order as a ferromagnet and to be electrically tunable as a semiconductor. Here, we demonstrate the electrical control of the exchange coupling in a hybrid consisting of a ferromagnetic Co layer and a semiconductor CdTe quantum well, separated by a thin non-magnetic (Cd,Mg)Te barrier. The electric field controls the phononic ac Stark effect-the indirect exchange mechanism that is mediated by elliptically polarized phonons emitted from the ferromagnet. The effective magnetic field of the exchange interaction reaches up to 2.5 Tesla and can be turned on and off by application of 1V bias across the heterostructure.

Discretization of the total magnetic field by the nuclear spin bath in fluorine-doped ZnSe.

The coherent spin dynamics of fluorine donor-bound electrons in ZnSe induced by pulsed optical excitation is studied in a perpendicular applied magnetic field. The Larmor precession frequency serves as a measure for the total magnetic field exerted onto the electron spins and, surprisingly, does not increase linearly with the applied field, but shows a step-like behavior with pronounced plateaus, given by multiples of the laser repetition rate. This discretization occurs by a feedback mechanism in which the electron spins polarize the nuclear spins, which in turn generate a local Overhauser field adjusting the total magnetic field accordingly. Varying the optical excitation power, we can control the plateaus, in agreement with our theoretical model. From this model, we trace the observed discretization to the optically induced Stark field, which causes the dynamic nuclear polarization.

Lessons learnt from school-based health promotion projects in low- and middle-income countries.

BACKGROUND: Non-communicable diseases (NCD) are now the leading cause of death worldwide. As habits and lifestyle are established in childhood and adolescence, targeting school children before they develop unhealthy habits offers a window of opportunity to halt and reverse the emerging NCD epidemic. However, few experiences from school interventions in low- and middle-income countries have been collected. Therefore, the aim of this study was to review experiences of implementing school-based health promotion interventions to identify barriers and recommendations for future interventions. METHODS: A qualitative investigation of 17 school-based health promotion interventions in low- and middle-income countries was conducted. Data were collected through questionnaires (15 project leaders) and in-depth interviews with nine project leaders. The data from the questionnaires and interviews was triangulated and analysed using content analysis, where themes and categories emerging from the material were explored. RESULTS: Three key themes emerged from the data: 1) policy environment and stakeholder engagement, 2) health education sessions, and 3) practical health promotion activities. The themes explored the experiences and lessons learned from 17 school-based health promotion projects in low- and middle-income countries. Stakeholders at different administrative levels were important for the projects; however, stakeholders close to implementation were seen to be more engaged. Most projects conducted traditional health education lectures, which formed the basis of their intervention. Promotion of physical activity and healthy eating through participatory approaches were identified; however, barriers such as lack of areas suitable for physical activity and lack of healthy food alternatives in schools can obstruct the successful implementation of interventions. CONCLUSIONS: This study has documented experiences with school-based health promotion in low- and middle-income countries, and has shown that schools can play an important role in facilitating NCD-related behavioural change in children. The study recommends increased emphasis on a whole-school approach where activities focusing on individual behavioural change are supported by interventions improving the structural environment.

[Vertebral tuberculosis in a chronic hemodialysis patient with polycystic kidney disease]. / Spondylite tuberculeuse chez une hémodialysée chronique porteuse d'une polykystose.

We report a case of vertebral tuberculosis in a female patient with polycystic kidney disease (PKD) who had been treated with maintenance hemodialysis for six years. Diagnosis of lumbar bacillary spondylitis was particularly difficult, owing to proximity of polycystic kidneys and spine. After removal of one kidney in which no bacterial focus was found, pain and inflammation persisted. Two months later CT scan and RMN evidence of 4th lumbar vertebral lysis led to performing open vertebral biopsy. Tuberculous lesions were found on this material and antibacillary treatment was begun. This case illustrates the difficulty of diagnosing vertebral tuberculosis in dialysis patients, especially in those with PKD.

[Prevention of peritonitis during continuous ambulatory peritoneal dialysis. Value of disconnectable systems]. / Prévention des péritonites au cours de la dialyse péritonéale continue ambulatoire. Intérêt des systèmes déconnectables.

Peritonitis remains the major obstacle to the acceptance of continuous ambulatory peritoneal dialysis as a long-term dialysis technique. In January, 1985, Y connectors were introduced into our continuous ambulatory peritoneal dialysis programme, and a two-year prospective randomized trial for all new patients was initiated in which the Y connection system was compared with the conventional technique in the prevention of peritonitis (group I). At the same time, 16 patients (group II), with a high incidence of peritonitis episodes were switched from the conventional technique to the Y connection system, while 55 patients (group III), remained on the conventional technique. Group IA patients (27 new patients using the Y connection system), developed peritonitis every 23 patient-months. Group IB patients (28 new patients using the conventional technique), developed peritonitis every 12.2 patient-months. The difference between these two sub-groups was statistically significant (P less than 0.02). Before their transfer to the Y connection system, group II patients developed peritonitis every 10 patient-months and thereafter one every 24 patient-months (P less than 0.001). Group III patients were divided into 12 continuous cyclic peritoneal dialysis patients with peritonitis every 24 patients-months, and 43 continuous ambulatory peritoneal dialysis patients with peritonitis every 11.7 patient-months. The Y connector therefore proved to be a simple and safe procedure effective in reducing the peritonitis rate in patients on continuous ambulatory peritoneal dialysis.

Role of distinctive features in dichotic perception of 21 English consonants.

The role distinctive features played in the identification of 21 dichotically presented syllable initial English consonants was evaluated. Results were analyzed for the entire stimulus set and for various intra- and inter-manner class comparisons. Consistent with previous dichotic studies of stops alone, stops as a subgroup showed a large right ear advantage, a high incidence of blend errors, and greater accuracy in identification when the competing stimuli contrasted on one (rather than two) distinctive features. Results for manner classes other than stops, for inter-manner comparisons and for the total stimulus set indicated increased correct identification with increasing numbers of distinctive feature differences between the two syllables. Analysis of error patterns revealed that, in addition to the stops, continuants, and stop-continuant, stop-affricate, and stop-nasal pairs revealed significant numbers of blend errors. Error responses also showed a tendency for unmarked feature specifications to predominate significantly over marked feature specifications. Finally, the magnitude of the right ear advantage varied significantly as a function of manner class, but not as a function of number of feature contrasts.