Local negative permittivity and topological phase transition in polar skyrmions.

Topological solitons such as magnetic skyrmions have drawn attention as stable quasi-particle-like objects. The recent discovery of polar vortices and skyrmions in ferroelectric oxide superlattices has opened up new vistas to explore topology, emergent phenomena and approaches for manipulating such features with electric fields. Using macroscopic dielectric measurements, coupled with direct scanning convergent beam electron diffraction imaging on the atomic scale, theoretical phase-field simulations and second-principles calculations, we demonstrate that polar skyrmions in (PbTiO3)n/(SrTiO3)n superlattices are distinguished by a sheath of negative permittivity at the periphery of each skyrmion. This enhances the effective dielectric permittivity compared with the individual SrTiO3 and PbTiO3 layers. Moreover, the response of these topologically protected structures to electric field and temperature shows a reversible phase transition from the skyrmion state to a trivial uniform ferroelectric state, accompanied by large tunability of the dielectric permittivity. Pulsed switching measurements show a time-dependent evolution and recovery of the skyrmion state (and macroscopic dielectric response). The interrelationship between topological and dielectric properties presents an opportunity to simultaneously manipulate both by a single, and easily controlled, stimulus, the applied electric field.

Programmable quantum emitter formation in silicon.

Silicon-based quantum emitters are candidates for large-scale qubit integration due to their single-photon emission properties and potential for spin-photon interfaces with long spin coherence times. Here, we demonstrate local writing and erasing of selected light-emitting defects using femtosecond laser pulses in combination with hydrogen-based defect activation and passivation at a single center level. By choosing forming gas (N2/H2) during thermal annealing of carbon-implanted silicon, we can select the formation of a series of hydrogen and carbon-related quantum emitters, including T and Ci centers while passivating the more common G-centers. The Ci center is a telecom S-band emitter with promising optical and spin properties that consists of a single interstitial carbon atom in the silicon lattice. Density functional theory calculations show that the Ci center brightness is enhanced by several orders of magnitude in the presence of hydrogen. Fs-laser pulses locally affect the passivation or activation of quantum emitters with hydrogen for programmable formation of selected quantum emitters.

All-electrical nuclear spin polarization of donors in silicon.

We demonstrate an all-electrical donor nuclear spin polarization method in silicon by exploiting the tunable interaction of donor bound electrons with a two-dimensional electron gas, and achieve over two orders of magnitude nuclear hyperpolarization at T=5 K and B=12 T with an in-plane magnetic field. We also show an intricate dependence of nuclear polarization effects on the orientation of the magnetic field, and both hyperpolarization and antipolarization can be controllably achieved in the quantum Hall regime. Our results demonstrate that donor nuclear spin qubits can be initialized through local gate control of electrical currents without the need for optical excitation, enabling the implementation of nuclear spin qubit initialization in dense multiqubit arrays.

Electrically detected magnetic resonance of neutral donors interacting with a two-dimensional electron gas.

We have measured the electrically detected magnetic resonance of donor-doped silicon field-effect transistors in resonant X- (9.7 GHz) and W-band (94 GHz) microwave cavities. The two-dimensional electron gas resonance signal increases by 2 orders of magnitude from X to W band, while the donor resonance signals are enhanced by over 1 order of magnitude. Bolometric effects and spin-dependent scattering are inconsistent with the observations. We propose that polarization transfer from the donor to the two-dimensional electron gas is the main mechanism giving rise to the spin resonance signals.

Chemical Raman enhancement of organic adsorbates on metal surfaces.

Using first-principles theory and experiments, chemical contributions to surface-enhanced Raman spectroscopy for a well-studied organic molecule, benzene thiol, chemisorbed on planar Au(111) surfaces are explained and quantified. Density functional theory calculations of the static Raman tensor demonstrate a strong mode-dependent modification of benzene thiol Raman spectra by Au substrates. Raman active modes with the largest enhancements result from stronger contributions from Au to their electron-vibron coupling, as quantified through a deformation potential. A straightforward and general analysis is introduced to extract chemical enhancement from experiments for specific vibrational modes; measured values are in excellent agreement with our calculations.

Engineering new limits to magnetostriction through metastability in iron-gallium alloys.

Magnetostrictive materials transduce magnetic and mechanical energies and when combined with piezoelectric elements, evoke magnetoelectric transduction for high-sensitivity magnetic field sensors and energy-efficient beyond-CMOS technologies. The dearth of ductile, rare-earth-free materials with high magnetostrictive coefficients motivates the discovery of superior materials. Fe1-xGax alloys are amongst the highest performing rare-earth-free magnetostrictive materials; however, magnetostriction becomes sharply suppressed beyond x = 19% due to the formation of a parasitic ordered intermetallic phase. Here, we harness epitaxy to extend the stability of the BCC Fe1-xGax alloy to gallium compositions as high as x = 30% and in so doing dramatically boost the magnetostriction by as much as 10x relative to the bulk and 2x larger than canonical rare-earth based magnetostrictors. A Fe1-xGax - [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (PMN-PT) composite magnetoelectric shows robust 90° electrical switching of magnetic anisotropy and a converse magnetoelectric coefficient of 2.0 × 10-5 s m-1. When optimally scaled, this high coefficient implies stable switching at ~80 aJ per bit.

Tunable Magnetoelastic Effects in Voltage-Controlled Exchange-Coupled Composite Multiferroic Microstructures.

The magnetoelectric properties of exchange-coupled Ni/CoFeB-based composite multiferroic microstructures are investigated. The strength and sign of the magnetoelastic effect are found to be strongly correlated with the ratio between the thicknesses of two magnetostrictive materials. In cases where the thickness ratio deviates significantly from one, the magnetoelastic behavior of the multiferroic microstructures is dominated by the thicker layer, which contributes more strongly to the observed magnetoelastic effect. More symmetric structures with a thickness ratio equal to one show an emergent interfacial behavior which cannot be accounted for simply by summing up the magnetoelastic effects occurring in the two constituent layers. This aspect is clearly visible in the case of ultrathin bilayers, where the exchange coupling drastically affects the magnetic behavior of the Ni layer, making the Ni/CoFeB bilayer a promising next-generation synthetic magnetic system entirely. This study demonstrates the richness and high tunability of composite multiferroic systems based on coupled magnetic bilayers compared to their single magnetic layer counterparts. Furthermore, because of the compatibility of CoFeB with present magnetic tunnel junction-based spintronic technologies, the reported findings are expected to be of great interest for the development of ultralow-power magnetoelectric memory devices.

Ultrafast dynamics at semiconductor and metal surfaces.

A variety of important dynamical phenomena at metal and semiconductor surfaces are now being investigated with the use of new ultrafast measurement techniques involving lasers and nonlinear optics. Understanding of the rates and mechanisms for relaxation of optical excitations of the surface itself as well as those of adsorbates on the surface is providing new insight into surface chemistry, surface phase transitions, and surface recombination of charge carriers in semiconductors.

Large resistivity modulation in mixed-phase metallic systems.

In numerous systems, giant physical responses have been discovered when two phases coexist; for example, near a phase transition. An intermetallic FeRh system undergoes a first-order antiferromagnetic to ferromagnetic transition above room temperature and shows two-phase coexistence near the transition. Here we have investigated the effect of an electric field to FeRh/PMN-PT heterostructures and report 8% change in the electrical resistivity of FeRh films. Such a 'giant' electroresistance (GER) response is striking in metallic systems, in which external electric fields are screened, and thus only weakly influence the carrier concentrations and mobilities. We show that our FeRh films comprise coexisting ferromagnetic and antiferromagnetic phases with different resistivities and the origin of the GER effect is the strain-mediated change in their relative proportions. The observed behaviour is reminiscent of colossal magnetoresistance in perovskite manganites and illustrates the role of mixed-phase coexistence in achieving large changes in physical properties with low-energy external perturbation.

5'-triphosphate recycles independently of acetylcholine in cholinergic synaptic vesicles.

The effect of hemicholinium-3 (HC-3) on vesicular contents in acetylcholine (ACh) and 5-triphosphate (ATP) and the vesicular incorporation of 14C-label derived from [14C]choline ,nd 3H-label derived from [3H]adenosine was investigated after low frequency stimulation (with a subsequent rest period) of the Torpedo electric organ. HC-3 (100 microM) caused an increased depletion of vesicular ACh and blocked the incorporation of 14C-label whereas contents in vesicular ATP and 3H-incorporation were identical with and without HC-3. HC-3 also blocked the recovery of electrical response of the tissue after stimulation but did not cause a change in vesicle numbers. The result suggest that synaptic vesicles continue to recycle ATP in the absence of recycling of ACh and that vesicular uptake and storage of the two components are not coupled to each other.

Bilateral thrombosis of the transverse sinuses: microsurgical revascularization with venous bypass.

The present paper reports a case of intracranial hypertension secondary to thrombophlebitis of the two transverse sinuses and internal jugular veins in which microsurgical revascularization was attempted. This was carried out by means of a bypass graft inserted between the right transverse sinus and the superficial jugular vein. As early as the first post-operative week, intracranial pressure improved and visual disorders regressed. This type of venous revascularization using microsurgical techniques should contribute to more successful and lasting results in cases of sinus occlusions of thrombophlebitic, traumatic or tumorous origins.

[Dysmorphic syndrome and vascular dysplasia: an atypical form of type IV Ehlers-Danlos syndrome]. / Syndrome dysmorphique et dysplasie vasculaire: une forme atypique d'Ehlers-Danlos type IV.

A 29 year old woman was hospitalized for the successive onset of extremely serious vascular accidents: rupture of the gastro-duodenal artery, aneurysm of the posterior tibial artery, discovery of bilateral carotid and vertebral aneurysm with development of a carotid-cavernous fistula. The patient had a very unusual morphotype with dwarfism, white hair and alopecia. Histological investigations failed to reveal atheromatous lesions and by contrast showed involvement of the skin (dermal atrophy) and in the blood vessels fibro-dysplasia of the media. This picture was suggestive of a vascular form of Ehlers-Danlos disease (Sack's syndrome or type IV Ehlers-Danlos disease). This syndrome is characterized by minor skin or joint manifestations replaced by arterial accidents (arterial rupture or development of aneurysms). The etiology is faulty maturation of procollagen III and the diagnosis is based upon fibroblast culture.

[Cerebrovascular complications of sickle-cell anemia]. / Complications cérébro-vasculaires de la drépanocytose.

Cerebrovascular disorders are frequent in sickle-cell anemia. They occur mainly in homozygous children. Traditionally, they were believed to result from an arteriolar sickle-cell thrombosis, the "sludge" phenomenon, which is generally responsible for sickle cell anemia disorders. It is now well known that several other kinds of cerebral damages are involved such as moya-moya syndrome, cerebral hemorrhage, subdural hematoma, extra-dural hematoma and cerebral thrombophlebitis. In this disease, the identification of these different processes cannot be always made by a simple clinical examination. However, specific therapies are sometimes necessary, such as neurosurgical intervention in the case of aneurysm or hematoma, and, according to some authors, the necessity of repeated appropriate transfusions, in the case of moya-moya. So it is imperative to carry out without delay a complete neuroradiological assessment of the lesions. At present, the most widely accepted theory to explain the arteriolar lesions, is that they result from a sickle-cell thrombosis of the vasa-vasorum, but, we think it is not the only valid hypothesis and we think that other phenomena may be involved with a genetic factor (patients with connective tissue disorders may have a particular genotype), and with infectious or autoimmune or coagulation disorders, the latter being frequently observed in this disease.

[Rare anatomical form of spinal cord ependymoma: metastatic ependymoblastoma involving whole spinal axis]. / Une forme anatomique rare d'épendymome médullaire: d'épendymoblastome métastatique étendu à l'ensemble de l'axe spinal

The authors report a case of malignant ependymoma of the terminal medullary cone and the cauda equina, presenting at the stage of metastatic diffusion to the whole spinal axis. They stress the pathological interest of such a form and its extreme rarity.

[Cerebellopontine angle chondroma. A report of one personal case (author's transl)]. / Les chondromes de l'angle ponto-cérébelleux. A propos d'une observation personnelle.

The authors report 1 case of cerebellopontine angle chondroma. In the World literature 12 cases are already described. They insist on the difficulty of the diagnosis and on the length of clinical evolution (12 years). The CT Scan will certainly transform this pathology by early detection of small tumors at extra dural stage.

[Recurrences of supratentorial meningiomas. Apropos of 17 cases]. / Récidives de méningiomes sus tentoriels. A propos de 17 cas.

17 cases of recurrent meningiomas observed during a 10 years period are reviewed. Meningiomas with a second localisation different from the first were excluded from the study. The tumor recurrence occurred mostly during the first five years after the surgical procedure. One case with femoral and pulmonary metastasis is described. Several factors may play a role in the genesis of the recurrence: age, sex, the tumor localisation, CT scan, the importance of the tumor ablation, the histology. In almost all cases a radiotherapy was carried out after the second surgical procedure. This retrospective study suggests the need for multifactorial prospective analysis with clinical, paraclinical and fundamental factors. Such a study would be useful to precise the natural history of meningiomas.

[Case of giant intra-petrous and intra-cavernous internal carotid aneurysm in a child]. / Un cas d'anévrysme géant intra-pétreux et intra-caverneux de la carotide interne chez l'enfant

The authors report the case of an eight-year-old girl hospitalised for severe headache with paroxysmal left otalgia, vomiting, aprexia, paralysis of the left 6 th cranial nerve and slight left facial weakness. Left carotid arteriography revealed a very large aneurysm of the internal carotid, involving its entire intra-petrous and intra-cavernous course. Treatment consisted of ligation of the internal carotid in the neck. Postoperative angiographic studies showed complete exclusion of the aneurysm, and it was unecessary to carry out "trapping" by ligation of the supra-cavernous carotid, as had initially been envisaged. The postoperative course was uneventful : immediate disappearance of otalgia, secondary complete recovery of the oculo-motor involvement and facial paresis. The absence of any infections or traumatic past history, together with the young age of the patient, represent arguments in favour of the congenital origin of this intra-petrous carotid aneurysm.

Mapping local charge recombination heterogeneity by multidimensional nanospectroscopic imaging.

As materials functionality becomes more dependent on local physical and electronic properties, the importance of optically probing matter with true nanoscale spatial resolution has increased. In this work, we mapped the influence of local trap states within individual nanowires on carrier recombination with deeply subwavelength resolution. This is achieved using multidimensional nanospectroscopic imaging based on a nano-optical device. Placed at the end of a scan probe, the device delivers optimal near-field properties, including highly efficient far-field to near-field coupling, ultralarge field enhancement, nearly background-free imaging, independence from sample requirements, and broadband operation. We performed ~40-nanometer-resolution hyperspectral imaging of indium phosphide nanowires via excitation and collection through the probes, revealing optoelectronic structure along individual nanowires that is not accessible with other methods.

Electrically detected magnetic resonance in a W-band microwave cavity.

We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94 GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7 GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity.