Flat Electronic Bands in Long Sequences of Rhombohedral-stacked Multilayer Graphene

The crystallographic stacking order in multilayer graphene plays an important role in determining its electronic properties. It has been predicted that a rhombohedral (ABC) stacking displays a conducting surface state with flat electronic dispersion. In such a flat band, the role of electron-electron correlation is enhanced possibly resulting in high Tc superconductivity, charge density wave or magnetic orders. Clean experimental band structure measurements of ABC stacked specimens are missing because the samples are usually too small in size. Here, we directly image the band structure of large multilayer graphene flake containing approximately 14 consecutive ABC layers. Angle-resolved photoemission spectroscopy experiments reveal the flat electronic bands near the K point extends by 0.13 {\AA}-1 at the Fermi level at liquid nitrogen temperature. First-principle calculations identify the electronic ground state as an antiferromagnetic state with a band gap of about 40 meV

Antiferromagnetic metal phase in an electron-doped rare-earth nickelate

Long viewed as passive elements, antiferromagnetic materials have emerged as promising candidates for spintronic devices due to their insensitivity to external fields and potential for high-speed switching. Recent work exploiting spin and orbital effects has identified ways to electrically control and probe the spins in metallic antiferromagnets, especially in noncollinear or noncentrosymmetric spin structures. The rare earth nickelate NdNiO3 is known to be a noncollinear antiferromagnet where the onset of antiferromagnetic ordering is concomitant with a transition to an insulating state. Here, we find that for low electron doping, the magnetic order on the nickel site is preserved while electronically a new metallic phase is induced. We show that this metallic phase has a Fermi surface that is mostly gapped by an electronic reconstruction driven by the bond disproportionation. Furthermore, we demonstrate the ability to write to and read from the spin structure via a large zero-field planar Hall effect. Our results expand the already rich phase diagram of the rare-earth nickelates and may enable spintronics applications in this family of correlated oxides.Comment: 25 pages, 4 figure

Magnetic gap opening in rhombohedral-stacked multilayer graphene from first principles

We investigate the occurrence of magnetic and charge density wave instabilities in rhombohedral-stacked multilayer (three to eight layers) graphene by first principles calculations including exact exchange. Neglecting spin polarization, an extremely flat surface band centered at the special point K of the Brillouin zone occurs at the Fermi level. Spin polarization opens a gap in the surface state by stabilizing an antiferromagnetic state. The top and the bottom surface layers are weakly ferrimagnetic in-plane (net magnetization smaller than 10(-3) mu B) and are antiferromagnetic coupled to each other. This coupling is propagated by the out-of-plane antiferromagnetic coupling between the nearest neighbors. The gap is very small in a spin-polarized generalized gradient approximation, while it is proportional to the amount of exact exchange in hybrid functionals. For trilayer rhombohedral graphene it is 38.6 meV in PBE0, in agreement with the 42 meV gap found in experiments. We study the temperature and doping dependence of the magnetic gap. At electron doping of n similar to 7 x 10(11) cm(-2) the gap closes. Charge density wave instabilities with root 3 x root 3 periodicity do not occur

Spin susceptibility and electron-phonon coupling of two-dimensional materials by range-separated hybrid density functionals: Case study of LixZrNCl

We investigate the capability of density functional theory (DFT) to appropriately describe the spin susceptibility, chi(s), and the intervalley electron-phonon coupling in LixZrNCl. At low doping, LixZrNCl behaves as a two-dimensional two-valley electron gas, with parabolic bands. In such a system, chi(s) increases with decreasing doping because of the electron-electron interaction. We show that DFT with local functionals (LDA/GGA) is not capable of reproducing this behavior. The use of exact exchange in Hartree-Fock (HF) or in DFT hybrid functionals enhances chi(s). HF, B3LYP, and PBE0 approaches overestimate chi(s), whereas the range-separated HSE06 functional leads to results similar to those obtained in the random phase approximation (RPA) applied to a two-valley two-spin electron gas. Within HF, LixZrNCl is even unstable towards a ferromagnetic state for x < 0.16. The intervalley phonons induce an imbalance in the valley occupation that can be viewed as the effect of a pseudomagnetic field. Thus, similarly to what happens for chi(s), the electron-phonon coupling of intervalley phonons is enhanced by the electron-electron interaction. Only hybrid DFT functionals capture such an enhancement and the HSE06 functional reproduces the RPA results presented in M. Calandra et al. [Phys. Rev. Lett. 114, 077001 (2015)]. These results imply that the description of the susceptibility and electron-phonon coupling with a range-separated hybrid functional would be important also in other two-dimensional weakly doped semiconductors, such as transition-metal dichalcogenides and graphene

The association of outer retinal tubulation with vitreomacular adhesion and epiretinal membrane in eyes with age-related macular degeneration

Aim of this study to investigate the relationship between outer retinal tubulation (ORT) and vitreomacular adhesion (VMA) or epiretinal membrane (ERM) in eyes with age-related macular degeneration (ARMD). 251 eyes of 138 (46 female, 92 male) patients were included in the study. Of those, 84 eyes were with dry type ARMD, 167 eyes were with wet type ARMD. Medical records of the cases were evaluated retrospectively. Evaluation of the vitreomacular interface (including VMA and ERM), and ORT was checked by using optical coherence tomography. VMA was observed in 26 eyes of 251 eyes and ERM in 46 of 251 eyes. In eyes with VMA, while ORT was not found in dry type ARMD, ORT was found in 5 (29.4%) of 17 eyes with wet type ARMD. In eyes with ERM, while ORT was found in one of 13 eyes (7.7%) with dry type ARMD, ORT was found in 6 (18.2%) of 33 eyes with wet type ARMD. No statistically significant difference was found between ORT presence and ERM or VMA presence in dry or wet type ARMD patients (p&#8805;0.05). Our study results suggest that, although there is no correlation between VMA and ERM with development of ORT in ARMD, further large-scale studies are required to confirm these findings and to establish a definite conclusion. [Med-Science 2020; 9(2.000): 423-6

Factors Affecting The Preference Of Anesthesia Residents Regarding Subspecialty Training

Background There is scant information about the factors that influence the career decisions of anesthesia residents in Turkey. The aim of this study was to determine the preferences of anesthesia residents in Turkey regarding future career and subspecialty training plans and practice location, and to determine the factors that influence those preferences. Methods A 21-item e-questionnaire was administered to anesthesia residents who were registered with at least one of the two societies of anesthesiologists in Turkey. Data were collected on demographics and preferences regarding subspecialty training and future practice location. Results The response rate of the survey was 41.04%. The percentages of participants who intended to pursue a fellowship in intensive care and algology were 12.1 and 23.1%, respectively; 21.7% of participants did not intend to pursue any fellowship training and the decision of 43.1% of the participants was uncertain. The most popular reasons for pursuing a fellowship were to perform compulsory service in a better place (47.2%) and improve earning potential (43.1%). Forty-two percent of participants did not intend to pursue any fellowship training because of their attention to general anesthesiology practice and 15.2% because of the additional compulsory service obligation following the training. Conclusions This study showed that the desirability of sub-specialization among anesthesia residents in Turkey could be accepted as low. This result seems to be associated with the additional compulsory service obligation. Electronic supplementary material The online version of this article (10.1186/s12909-019-1782-9) contains supplementary material, which is available to authorized users.PubMedWoSScopu

An international SUrvey on non-iNvaSive tecHniques to assess the mIcrocirculation in patients with RayNaud'\u80\u99s phEnomenon (SUNSHINE survey)

To canvas opinion concerning the role of non-invasive techniques in the assessment of patients with Raynaud's phenomenon (Rp) in clinical and research settings: four nailfold capillaroscopy methods [videocapillaroscopy (NVC), dermoscopy, stereomicroscopy, digital USB microscopy], four laser Doppler methods (laser Doppler flowmetry, imaging, anemometry/velocimetry, laser speckle contrast analysis), thermographic imaging, and upper limb arterial Doppler ultrasound. Emails with a link to the survey were sent to physicians from the European Scleroderma Trials and Research group (EUSTAR), the EULAR Study Group on Microcirculation in Rheumatic Diseases (SG_MC/RD) and members of the pediatric rheumatology Email board. The main descriptive analysis related to physicians looking after adult patients, with some analysis also of opinions from paediatric rheumatologists. 106 'adult physicians' responded (a response rate of 25.8%), of whom 68.9% were European, and 81.1% practising for more than 10 years. Nineteen paediatricians responded. The most widely available technique was NVC (72.7%). Nailfold capillaroscopy was most frequently performed by the physician him/herself, using different types of equipment relating to availability. Most rheumatologists reported high levels of appropriateness for NVC in both clinical and research settings for global assessment and differential diagnosis of Rp. Other techniques were less used. Of all the different techniques, nailfold capillaroscopy was the one most used in both clinical and research settings by adult physicians, the majority of whom use NVC in their everyday practice. The low proportion of clinicians using other techniques suggests that these are currently mainly research tools, available only in specialist centres

Proceedings Of The 23Rd Paediatric Rheumatology European Society Congress: Part Two

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