Observation of room-temperature polar skyrmions.

Complex topological configurations are fertile ground for exploring emergent phenomena and exotic phases in condensed-matter physics. For example, the recent discovery of polarization vortices and their associated complex-phase coexistence and response under applied electric fields in superlattices of (PbTiO3)n/(SrTiO3)n suggests the presence of a complex, multi-dimensional system capable of interesting physical responses, such as chirality, negative capacitance and large piezo-electric responses1-3. Here, by varying epitaxial constraints, we discover room-temperature polar-skyrmion bubbles in a lead titanate layer confined by strontium titanate layers, which are imaged by atomic-resolution scanning transmission electron microscopy. Phase-field modelling and second-principles calculations reveal that the polar-skyrmion bubbles have a skyrmion number of +1, and resonant soft-X-ray diffraction experiments show circular dichroism, confirming chirality. Such nanometre-scale polar-skyrmion bubbles are the electric analogues of magnetic skyrmions, and could contribute to the advancement of ferroelectrics towards functionalities incorporating emergent chirality and electrically controllable negative capacitance.

Metric fixed point theory and partial impredicativity.

We show that the Priess-Crampe & Ribenboim fixed point theorem is provable in [Formula: see text]. Furthermore, we show that Caristi's fixed point theorem for both Baire and Borel functions is equivalent to the transfinite leftmost path principle, which falls strictly between [Formula: see text] and [Formula: see text]. We also exhibit several weakenings of Caristi's theorem that are equivalent to [Formula: see text] and to [Formula: see text]. This article is part of the theme issue 'Modern perspectives in Proof Theory'.

Observation of polar vortices in oxide superlattices.

The complex interplay of spin, charge, orbital and lattice degrees of freedom provides a plethora of exotic phases and physical phenomena. In recent years, complex spin topologies have emerged as a consequence of the electronic band structure and the interplay between spin and spin-orbit coupling in materials. Here we produce complex topologies of electrical polarization--namely, nanometre-scale vortex-antivortex (that is, clockwise-anticlockwise) arrays that are reminiscent of rotational spin topologies--by making use of the competition between charge, orbital and lattice degrees of freedom in superlattices of alternating lead titanate and strontium titanate layers. Atomic-scale mapping of the polar atomic displacements by scanning transmission electron microscopy reveals the presence of long-range ordered vortex-antivortex arrays that exhibit nearly continuous polarization rotation. Phase-field modelling confirms that the vortex array is the low-energy state for a range of superlattice periods. Within this range, the large gradient energy from the vortex structure is counterbalanced by the corresponding large reduction in overall electrostatic energy (which would otherwise arise from polar discontinuities at the lead titanate/strontium titanate interfaces) and the elastic energy associated with epitaxial constraints and domain formation. These observations have implications for the creation of new states of matter (such as dipolar skyrmions, hedgehog states) and associated phenomena in ferroic materials, such as electrically controllable chirality.

Benefits of the epilepsy specialist nurses (ESN) role, standardized practices and education around the world.

Epilepsy, often considered as a stigmatizing disease, affects 65 million people worldwide and is frequently associated with comorbidities that increase both direct and indirect costs. The degree of impact on quality of life and the cost of care differs depending on the social and health care organizations in place, political, medico-economic and/or socio-cultural contexts. Across the globe, healthcare is provided by nurses in primary care, urgent or emergency care, and within specialized domains of practice. In Epilepsy the global care could be enhanced by developing standardized nursing education in close collaboration with other caregivers. The impact of epilepsy nursing care has been documented in some developed countries, but the diversity of nursing practices and professional education of nurses raise difficulties in generalizing these findings. Specialized education in epilepsy will improve access, treatment and ultimately the quality of life of patients.

Disentangled Cooperative Orderings in Artificial Rare-Earth Nickelates.

Coupled transitions between distinct ordered phases are important aspects behind the rich phase complexity of correlated oxides that hinder our understanding of the underlying phenomena. For this reason, fundamental control over complex transitions has become a leading motivation of the designer approach to materials. We have devised a series of new superlattices by combining a Mott insulator and a correlated metal to form ultrashort period superlattices, which allow one to disentangle the simultaneous orderings in RENiO_{3}. Tailoring an incommensurate heterostructure period relative to the bulk charge ordering pattern suppresses the charge order transition while preserving metal-insulator and antiferromagnetic transitions. Such selective decoupling of the entangled phases resolves the long-standing puzzle about the driving force behind the metal-insulator transition and points to the site-selective Mott transition as the operative mechanism. This designer approach emphasizes the potential of heterointerfaces for selective control of simultaneous transitions in complex materials with entwined broken symmetries.

Decoupling Carrier Concentration and Electron-Phonon Coupling in Oxide Heterostructures Observed with Resonant Inelastic X-Ray Scattering.

We report the observation of multiple phonon satellite features in ultrathin superlattices of the form nSrIrO_{3}/mSrTiO_{3} using resonant inelastic x-ray scattering (RIXS). As the values of n and m vary, the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the RIXS cross section, we extract the variation in the electron-phonon coupling strength as a function of n and m. Combined with the negligible carrier doping into the SrTiO_{3} layers, these results indicate that the tuning of the electron-phonon coupling can be effectively decoupled from doping. This work both showcases a feasible method to extract the electron-phonon coupling in superlattices and unveils a potential route for tuning this coupling, which is often associated with superconductivity in SrTiO_{3}-based systems.

Magnetic Interactions at the Nanoscale in Trilayer Titanates.

We report on the phase diagram of competing magnetic interactions at the nanoscale in engineered ultrathin trilayer heterostructures of LaTiO_{3}/SrTiO_{3}/YTiO_{3}, in which the interfacial inversion symmetry is explicitly broken. Combined atomic layer resolved scanning transmission electron microscopy with electron energy loss spectroscopy and electrical transport have confirmed the formation of a spatially separated two-dimensional electron liquid and high density two-dimensional localized magnetic moments at the LaTiO_{3}/SrTiO_{3} and SrTiO_{3}/YTiO_{3} interfaces, respectively. Resonant soft x-ray linear dichroism spectroscopy has demonstrated the presence of orbital polarization of the conductive LaTiO_{3}/SrTiO_{3} and localized SrTiO_{3}/YTiO_{3} electrons. Our results provide a route with prospects for exploring new magnetic interfaces, designing a tunable two-dimensional d-electron Kondo lattice, and potential spin Hall applications.

Direct Detection of Pure ac Spin Current by X-Ray Pump-Probe Measurements.

Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (Ni_{81}Fe_{19}) layer in a Py/Cu/Cu_{75}Mn_{25}/Cu/Co multilayer to pump a pure ac spin current into the Cu_{75}Mn_{25} and Co layers, and then directly probe the spin current within the Cu_{75}Mn_{25} layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the Cu_{75}Mn_{25} layer.

Correlation-Driven Insulator-Metal Transition in Near-Ideal Vanadium Dioxide Films.

We use polarization- and temperature-dependent x-ray absorption spectroscopy, in combination with photoelectron microscopy, x-ray diffraction, and electronic transport measurements, to study the driving force behind the insulator-metal transition in VO_{2}. We show that both the collapse of the insulating gap and the concomitant change in crystal symmetry in homogeneously strained single-crystalline VO_{2} films are preceded by the purely electronic softening of Coulomb correlations within V-V singlet dimers. This process starts 7 K (±0.3 K) below the transition temperature, as conventionally defined by electronic transport and x-ray diffraction measurements, and sets the energy scale for driving the near-room-temperature insulator-metal transition in this technologically promising material.

Risk of adverse events on epilepsy monitoring units: a survey of epilepsy professionals.

In 2008 a workgroup of health care professionals from the American Epilepsy Society (AES) was convened to address the lack of consensus regarding patient care in epilepsy monitoring units (EMUs). The group developed a questionnaire designed to identify the extent to which selected adverse events occurred in EMUs, and it was sent via email to all members of the AES. We asked that only one representative from each center report. Seventy responses were received. The number of centers reporting the following adverse events included: falls by 69%, status epilepticus by 63%, and postictal psychosis by 54%. Infrequent events with serious consequences were also reported including pneumonia by 10%, cardiac arrest by 7%, fractures by 6%, and death by 3% (N=2). Of the 58 respondents who reported using intracranial electrodes, 37.9% (N=22) reported that patients pulled out or dislodged electrodes. This study highlights the need for EMUs to identify and address potential safety risks in their environment, patient population, and system of care.

Creation of skyrmions in van der Waals ferromagnet Fe3GeTe2 on (Co/Pd) n superlattice.

Magnetic skyrmions are topological spin textures, which usually exist in noncentrosymmetric materials where the crystal inversion symmetry breaking generates the so-called Dzyaloshinskii-Moriya interaction. This requirement unfortunately excludes many important magnetic material classes, including the recently found two-dimensional van der Waals (vdW) magnetic materials, which offer unprecedented opportunities for spintronic technology. Using photoemission electron microscopy and Lorentz transmission electron microscopy, we investigated and stabilized Néel-type magnetic skyrmion in vdW ferromagnetic Fe3GeTe2 on top of (Co/Pd) n in which the Fe3GeTe2 has a centrosymmetric crystal structure. We demonstrate that the magnetic coupling between the Fe3GeTe2 and the (Co/Pd) n could create skyrmions in Fe3GeTe2 without the need of an external magnetic field. Our results open exciting opportunities in spintronic research and the engineering of topologically protected nanoscale features by expanding the group of skyrmion host materials to include these previously unknown vdW magnets.

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.

Anomalous orbital structure in two-dimensional titanium dichalcogenides.

Generally, lattice distortions play a key role in determining the electronic ground states of materials. Although it is well known that trigonal distortions are generic to most two dimensional transition metal dichalcogenides, the impact of this structural distortion on the electronic structure and topological properties has not been understood conclusively. Here, by using a combination of polarization dependent X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and atomic multiplet cluster calculations, we have investigated the electronic structure of titanium dichalcogenides TiX2 (X = S, Se, Te), where the magnitude of the trigonal distortion increase monotonically from S to Se and Te. Our results reveal the presence of an anomalously large crystal field splitting. This unusual kind of crystal field splitting is likely responsible for the unconventional electronic structure of TiX2 compounds and ultimately controls the degree of the electronic phase protection. Our findings also indicate the drawback of the distorted crystal field picture in explaining the observed electronic ground state and emphasize the key importance of trigonal symmetry, metal-ligand hybridization and electron-electron correlations in defining the electronic structures at the Fermi energy.

Coherent ac spin current transmission across an antiferromagnetic CoO insulator.

The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. The question currently surrounding this topic is: whether and how could THz antiferromagnetic magnons mediate a GHz spin current? This mismatch of frequencies becomes particularly critical for the case of coherent ac spin current, raising the fundamental question of whether a GHz ac spin current can ever keep its coherence inside an antiferromagnetic insulator and so drive the spin precession of another ferromagnet layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001) heterostructures, here we demonstrate that a coherent GHz ac spin current pumped by the Py ferromagnetic resonance can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the Fe75Co25 layer. Further measurement results favor thermal magnons rather than evanescent spin waves as the mediator of the coherent ac spin current in CoO.

Nature of the metal-insulator transition in few-unit-cell-thick LaNiO3 films.

The nature of the metal-insulator transition in thin films and superlattices of LaNiO3 only a few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate-film interface quality may also affect the observable properties of ultrathin films. Here we report results obtained for near-ideal LaNiO3 films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO3 substrates. We find that the room-temperature metallic behavior persists until the film thickness is reduced to an unprecedentedly small 1.5 unit cells (NiO2 termination). Electronic structure measurements using X-ray absorption spectroscopy and first-principles calculation suggest that oxygen vacancies existing in the films also contribute to the metal-insulator transition.

Long-term tolerability, pharmacokinetic and preliminary efficacy study of lamotrigine in patients with resistant partial seizures.

Four adult men with resistant partial seizures underwent an intensive open-label protocol designed to evaluate long-term add-on lamotrigine (LTG) therapy. Following an 8-week baseline, LTG was added to their background medication(s) (carbamazepine in three; carbamazepine and phenytoin in one). Incremental LTG doses of 50, 100, 150, and 200 mg every 12 h were given on days 58-60, 61-63, 64-127, and 128-176, respectively. The patients were hospitalized during and after each of the dose increases for a total of 25 days. Frequent outpatient visits were performed biweekly, weekly, or monthly, depending on the phase of the protocol. Frequent clinical, electrocardiographic (ECG), and laboratory evaluations were performed. Serial blood levels and 24-h urine collections were performed sequentially. In patients 1, 2, and 3, LTG was well tolerated at 200 mg b.i.d. Patient 4 did not tolerate 150 mg, b.i.d., but tolerated and maintained complete seizure control on 100 b.i.d. All four patients tolerated LTG and continued to receive it for 39, 46, 105, and 104 weeks, respectively. Serial 12-h plasma LTG levels were obtained on days 63, 70, and 133. On these days, the mean (+/- SD) LTG clearances (dose/AUC) were 0.0436 +/- 0.0171, 0.0468 +/- 0.0093, and 0.0575 +/- 0.0160 L/h/kg, respectively. Some 43-87% of the LTG was recovered in the urine, predominantly as the glucuronide metabolite. In the four patients, the mean weekly seizure frequency per patient was 6.5 in baseline, 5.0 on submaximal LTG doses, and 3.5 on the maximum administered doses. Three of the four patients eventually experienced a greater than 50% decrease in seizure frequency. In conclusion, when given for long periods of time (9.5 months to 2 years), LTG was well tolerated in doses up to 400 mg/day and mean trough levels of 3.0 +/- 0.6 microgram/ml; LTG has a favorable pharmacokinetic profile and appears to exhibit first-order linear kinetics during long-term chronic dosing; LTG shows preliminary evidence of efficacy during long-term administration; and to date, our patients represent the longest reported experience of continuous and closely monitored LTG therapy in the literature.

New therapies in the management of acute or cluster seizures and seizure emergencies.

Acute repetitive seizures, also known as cluster or serial seizures, may present considerable health risks, including death, to patients with epilepsy and often are a cause of psychosocial stigma. Fortunately, new formulations and drug-delivery systems approved by the Food and Drug Administration (FDA) over the past 5 years offer patients and health care providers greater control over acute repetitive seizures and emergency situations. Drugs that can be given intravenously, such as diazepam, phenytoin and valproate sodium solution, typically have the most rapid onset but are limited to use in clinical settings by health care professionals authorized to use them. In contrast, diazepam rectal gel can be administered to patients by their caregivers or family members in the home or in other non-hospital settings. Studies have shown that rectal diazepam used in such settings can reduce the number of emergency room visits, costs associated with emergent care and stress on the patient and family. Health education is necessary to help patients and families understand new treatment options and use them successfully. Additionally, facilitating patient compliance with prescribed treatment regimens may reduce the frequency and consequences of seizure emergencies.

Epilepsy and seizures: advances in seizure assessment, treatment, and self-management.

The scope of providing care for people with epilepsy and seizures has expanded dramatically in recent years. The tremendous growth in our understanding, along with new and innovative treatment options has increased the likelihood of seizure control and improved quality of life for many people. The ability to more accurately diagnose seizures will be enhanced by new seizure assessment guidelines. A fuller appreciation of the patient's perspective will aid nurses in their support of self-management practices. The new millennium will challenge nurses to enhance self-management education in more diverse practice settings, geographical areas, and patient populations.