The recent discovery of possible high-temperature (T(c)) superconductivity over 65 K in a monolayer FeSe film on SrTiO3 (refs 1-6) triggered a fierce debate on how superconductivity evolves from bulk ...to film, because bulk FeSe crystal exhibits a T(c) of no higher than 10 K (ref. 7). However, the difficulty in controlling the carrier density and the number of FeSe layers has hindered elucidation of this problem. Here, we demonstrate that deposition of potassium onto FeSe films markedly expands the accessible doping range towards the heavily electron-doped region. Intriguingly, we have succeeded in converting non-superconducting films with various thicknesses into superconductors with T(c) as high as 48 K. We also found a marked increase in the magnitude of the superconducting gap on decreasing the FeSe film thickness, indicating that the interface plays a crucial role in realizing the high-temperature superconductivity. The results presented provide a new strategy to enhance and optimize T(c) in ultrathin films of iron-based superconductors.
WKB theoretic transformation to the boosted Airy equation is discussed. The formulae for the discontinuities of the Borel transforms of the WKB solutions to a differential equation which can be ...transformed to the boosted Airy equation is given.
A topological insulator is an unusual quantum state of matter, characterized by the appearance, at its edges or on its surface, of a gapless metallic state that is protected by time-reversal ...symmetry. The discovery of topological insulators has stimulated the search for other topological states protected by other symmetries, such as the recently predicted topological crystalline insulator (TCI) in which the metallic surface states are protected by the mirror symmetry of the crystal. Here we present experimental evidence for the TCI phase in tin telluride (SnTe), which has been predicted to be a TCI (ref. ). Our angle-resolved photoemission spectra show the signature of a metallic Dirac-cone surface band, with its Dirac point slightly away from the edge of the surface Brillouin zone in SnTe. Such a gapless surface state is absent in a cousin material, lead telluride, in line with the theoretical prediction. PUBLICATION ABSTRACT
We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (T_{c}∼8 K), which exhibits a tetragonal-to-orthorhombic structural transition at T_{s}∼90 K. ...At low temperature, we found splitting of the energy bands as large as 50 meV at the M point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to T∼110 K, slightly above T_{s}, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe.
Summary
Background
Exertional heat illness (EHI) is recognised in horses, but few reports have investigated its risk factors.
Objectives
To identify risk factors for EHI in racehorses participating ...in flat races in Japan.
Study design
Descriptive epidemiology and retrospective unmatched case–control study.
Methods
Between 2005 and 2016, veterinary records of horses diagnosed with EHI after flat races were reviewed retrospectively and data of the months from April to September were used for a case–control study. For each case, three control horses were randomly selected from starts between April and September. Race records of horses and estimated wet‐bulb globe temperature (WBGT) indexes at the local meteorological observatory closest to the racecourse were investigated. To identify risk factors for EHI, univariable and multivariable logistic regression analysis was used.
Results
Of 194 cases during the study period, 188 cases occurred between April and September. The highest incidence risk was in July (1.1 cases per 1000 starts, 95% confidence interval 0.84–1.45). In the final multivariable model, WBGT index, sex, race distance, age and bodyweight were associated with EHI. When WBGT index exceeded 28°C, the risk of EHI was considerably higher than <20°C (OR 28.5, 14.2–62.4, P<0.001). Compared with uncastrated males, geldings (OR 4.9, 1.8–13.3, p = 0.002) and females (OR 2.4, 1.5–3.7, P<0.001) were at high risk of EHI (P<0.01). Furthermore, races of >1600 m (OR 1.8, 1.2–2.8, P = 0.002), 4‐year‐old (OR 3.5, 1.6–7.9, P = 0.002) and ≥5‐year‐old (OR 3.9, 1.8–9.2, P = 0.001) horses and horses with low bodyweight (OR per 20 kg, 0.8, 0.7–1.0, P = 0.02) were associated with increased risk of EHI.
Main limitations
The median straight‐line distance between the racecourse and the local meteorological observatory was 14.2 km (range, 1.1–28.3 km). There was a lack of objective criteria of EHI due to the retrospective nature of the study.
Conclusions
We identified specific risk factors for EHI in racehorses. These results may be useful to the equine industry for reducing EHI occurrence in racehorses.
The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2's Small Carry-on Impactor. The impact ...produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. The ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. The crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. We discuss implications for Ryugu's surface age.
Abstract
The microphysical properties, such as effective viscosity and conductivity, of the weakly magnetized intergalactic plasma are not yet well known. We investigate the constraints that can be ...placed by an azimuthally resolved study of the cold front in Abell 3667 using ∼500 ks archival Chandra data. We find that the radius of the interface fluctuates with position angle and the morphology of the interface is strikingly similar to recent numerical simulations of inviscid gas-stripping. We find multiple edges in the surface brightness profiles across the cold front as well as azimuthal variations, which are consistent with the presence of Kelvin–Helmholtz instabilities (KHIs) developing along the cold front. They indicate that the characteristic length-scale of KHI rolls is around 20–80 kpc. This is the first observational indication of developing KHIs along a merger cold front in a galaxy cluster. Based on the KHI scenario, we estimated the upper limit of the intracluster medium effective viscosity. The estimated value of μ ≲ 200 g cm−1 s−1 is at most 5 per cent of the isotropic Spitzer-like viscosity. The observed apparent mixing towards the outer edges away from the tip of the front provides an additional evidence for suppressed viscosity.
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