Quasiparticle Liquid in the Highly Overdoped Bi2212

We present results from the study of a highly overdoped (OD) Bi2212 with a $T_{c}=51$K using high resolution angle-resolved photoemission spectroscopy. The temperature dependent spectra near the ($\pi,0$) point show the presence of the sharp peak well above $T_{c}$. From the nodal direction, we make comparison of the self-energy with the optimally doped and underdoped cuprates, and the Mo(110) surface state. We show that this OD cuprate appears to have properties that approach that of the Mo. Further analysis shows that the OD has a more $k$-independent lineshape at the Fermi surface than the lower-doped cuprates. This allows for a realistic comparison of the nodal lifetime values to the experimental resistivity measurements via Boltzmann transport formulation. All these observations point to the validity of the quasiparticle picture for the OD even in the normal state within a certain energy and momentum range.Comment: 4 pages, 4 figure

Quasiparticles in a strongly correlated liquid with the fermion condensate: applications to high-temperature superconductors

A model of a strongly correlated electron liquid based on the fermion condensation (FC) is extended to high-temperature superconductors. Within our model, the appearance of FC presents a boundary separating the region of a strongly interacting electron liquid from the region of a strongly correlated electron liquid. We study the superconductivity of a strongly correlated liquid and show that under certain conditions, the superconductivity vanishes at temperatures $T>T_c\simeq T_{node}$, with the superconducting gap being smoothly transformed into a pseudogap. As the result, the pseudogap occupies only a part of the Fermi surface. The gapped area shrinks with increasing the temperature and vanishes at $T=T^*$. The single-particle excitation width is also studied. The quasiparticle dispersion in systems with FC can be represented by two straight lines characterized by the respective effective masses $M^*_{FC}$ and $M^*_L$, and intersecting near the binding energy that is of the order of the superconducting gap. It is argued that this strong change of the quasiparticle dispersion at the binding can be enhanced in underdoped samples because of strengthening the FC influence. The FC phase transition in the presence of the superconductivity is examined, and it is shown that this phase transition can be considered as kinetic energy driven.Comment: 16 pages, 3 figures, minor grammatical changes, revised and accepted by JET

Considerations for nutrition support in critically ill children with COVID-19 and paediatric inflammatory multisystem syndrome temporally associated with COVID-19

The aim of this editorial is to provide an adaptation of nutrition support recommendations for the overall population of critically ill children, to provide further refined recommendations for critically ill children presenting with COVID-19 or paediatric hyper-inflammatory syndrome temporally associated with COVID-19. They are based on the ESPNIC-MEN section recommendations published in January 2020 (6) and Surviving Sepsis Campaign recommendations from February 2020 (7). These recommendations cover the acute, stable and rehabilitation phases (Table 1, Table 2)

Renormalization of spectral lineshape and dispersion below Tc in Bi2Sr2CaCu2O8+d

Angle-resolved photoemission (ARPES) data in the superconducting state of Bi2Sr2CaCu2O8+d show a kink in the dispersion along the zone diagonal, which is related via a Kramers-Kronig analysis to a drop in the low-energy scattering rate. As one moves towards (pi,0), this kink evolves into a spectral dip. The occurrence of these anomalies in the dispersion and lineshape throughout the zone indicate the presence of a new energy scale in the superconducting state.Comment: New Figure 3 with expanded discussio

PICU mortality of children with cancer admitted to pediatric intensive care unit : a systematic review and meta-analysis

Background: Outcomes for children diagnosed with cancer have improved dramatically over the past 20 years. However, although 40% of pediatric cancer patients require at least one intensive care admission throughout their disease course, PICU outcomes and resource utilization by this population have not been rigorously studied in this specific group. Methods: Using a systematic strategy, we searched Medline, Embase, and CINAHL databases for articles describing PICU mortality of pediatric cancer patients admitted to PICU. Two investigators independently applied eligibility criteria, assessed data quality, and extracted data. We pooled PICU mortality estimates using random-effects models and examined mortality trends over time using meta-regression models. Results: Out of 1218 identified manuscripts, 31 studies were included covering 16,853 PICU admissions with the majority being retrospective in nature. Overall pooled weighted mortality was 27.8% (95% confidence interval (CI), 23.7-31.9%). Mortality decreased slightly over time when post-operative patients were excluded. The use of mechanical ventilation (odds ratio (OR): 18.49 [95% CI 13.79-24.78], p < 0.001), inotropic support (OR: 14.05 [95% CI 9.16-21.57], p < 0.001), or continuous renal replacement therapy (OR: 3.24 [95% CI 1.31-8.04], p = 0.01) was significantly associated with PICU mortality. Conclusions: PICU mortality rates of pediatric cancer patients are far higher when compared to current mortality rates of the general PICU population. PICU mortality has remained relatively unchanged over the past decades, a slight decrease was only seen when post-operative patients were excluded. This compared infavorably with the improved mortality seen in adults with cancer admitted to ICU, where research-led improvements have led to the paradigm of unlimited, aggressive ICU management without any limitations on resuscitations status, for a time-limited trial

CDW, Superconductivity and Anomalous Metallic Behavior in 2D Transition Metal Dichalcogenides

We propose a theory for quasi-two-dimensional transition metal dichalcogenides that provides a unified microscopic picture of the charge density wave (CDW) and superconducting phases. We show, based on the electron-phonon coupling and Fermi surface topology, that a CDW order parameter with six-fold symmetry and nodes (f-wave) gives a consistent description of the available experimental data. The elementary excitations in the CDW phase are Dirac electrons. The superconducting state has its origin on the attractive interaction mediated by phonons. The theory predicts strong deviations from Fermi liquid theory in the CDW phase.Comment: 4 pages, 3 figure

Evidence for an energy scale for quasiparticle dispersion in Bi_2Sr_2CaCu_2O_8

Quasiparticle dispersion in $Bi_{2}Sr_{2}CaCu_{2}O_{8}$ is investigated with improved angular resolution as a function of temperature and doping. Unlike the linear dispersion predicted by the band calculation, the data show a sharp break in dispersion at $50\pm10$ $meV$ binding energy where the velocity changes by a factor of two or more. This change provides an energy scale in the quasiparticle self-energy. This break in dispersion is evident at and away from the d-wave node line, but the magnitude of the dispersion change decreases with temperature and with increasing doping.Comment: 4 figure

Magnetism of small V clusters embedded in a Cu fcc matrix: an ab initio study

We present extensive first principles density functional theory (DFT) calculations dedicated to analyze the magnetic and electronic properties of small V$_{n}$ clusters (n=1,2,3,4,5,6) embedded in a Cu fcc matrix. We consider different cluster structures such as: i) a single V impurity, ii) several V$_{2}$ dimers having different interatomic distance and varying local atomic environment, iii) V$_{3}$ and iv) V$_{4}$ clusters for which we assume compact as well as 2- and 1-dimensional atomic configurations and finally, in the case of the v) V$_{5}$ and vi) V$_{6}$ structures we consider a square pyramid and a square bipyramid together with linear arrays, respectively. In all cases, the V atoms are embedded as substitutional impurities in the Cu network. In general, and as in the free standing case, we have found that the V clusters tend to form compact atomic arrays within the cooper matrix. Our calculated non spin-polarized density of states at the V sites shows a complex peaked structure around the Fermi level that strongly changes as a function of both the interatomic distance and local atomic environment, a result that anticipates a non trivial magnetic behavior. In fact, our DFT calculations reveal, in each one of our clusters systems, the existence of different magnetic solutions (ferromagnetic, ferrimagnetic, and antiferromagnetic) with very small energy differences among them, a result that could lead to the existence of complex finite-temperature magnetic properties. Finally, we compare our results with recent experimental measurements.Comment: 7 pages and 4 figure

Absence of a pseudogap in the in-plane infrared response of Bi2Sr2CaCu2O(8+d)

The ab-plane reflectance of Bi2Sr2CaCu2O(8+d) thin films was measured in the 30-25000 cm^(-1) range for one underdoped (Tc = 70 K), and one overdoped sample (Tc = 63 K) as a function of temperature (10-300 K). We find qualitatively similar behaviors in the temperature dependence of the normal-state infrared response of both samples. Above Tc, the effective spectral weight, obtained from the integrated conductivity, does not decrease when T decreases, so that no opening of an optical pseudogap is seen. We suggest that these are consequences of the pseudogap opening first in the k=(0, pi) direction, according to ARPES, and of the in-plane infrared conductivity being mostly sensitive to the k=(pi, pi) direction.Comment: 11 pages, 3 figure