Search

Aims: To report a prospective two centred non-comparative interventional pilot study of a solution of perfluorohexyl-octane and silicone oil (Densiron-68) as a heavier than water internal tamponade. Methods: 42 consecutive patients were recruited. The indications include proliferative vitreoretinopathy, retinal detachments arising from inferior retinal breaks, and inability to posture. Results: The success rate with one operation using Densiron was 81% and with further surgery 93%. At the end of the study all tamponade agents were removed in 90% of patients. Visual acuity improved from mean logMAR of 1.41 (SD 0.64) to 0.94 (SD 0.57), p = 0.001. There was little evidence of dispersion and excessive inflammation. Conclusion: This new tamponade agent is being compared to conventional silicone oil in a prospective international randomised trial. [ABSTRACT FROM AUTHOR]

We report the observation of a nontrivial spin texture in Dirac node arcs, i.e., novel topological objects formed when Dirac cones of massless particles extend along an open one-dimensional line in momentum space. We find that such states are present in all the compounds of the tetradymite M2Te2X family (M=Ti, Zr, or Hf and X=P or As) regardless of the weak or strong character of the topological invariant. The Dirac node arcs in tetradymites are thus the simplest possible textbook example of a type-I Dirac system with a single spin-polarized node arc. [ABSTRACT FROM AUTHOR]

We report a de Haas-van Alphen (dHvA) effect study on the Dirac type-II semimetallic candidates MAl3 (where, M=V, Nb and Ta). The angular dependence of their Fermi surface (FS) cross-sectional areas reveals a remarkably good agreement with our first-principles calculations. Therefore, dHvA supports the existence of tilted Dirac cones with Dirac type-II nodes located at 100, 230 and 250 meV above the Fermi level ϵF for VAl3, NbAl3 and TaAl3 respectively, in agreement with the prediction of broken Lorentz invariance in these compounds. However, for all three compounds we find that the cyclotron orbits on their FSs, including an orbit nearly enclosing the Dirac type-II node, yield trivial Berry phases. We explain this via an analysis of the Berry phase where the position of this orbit, relative to the Dirac node, is adjusted within the error implied by the small disagreement between our calculations and the experiments. We suggest that a very small amount of doping could displace ϵF to produce topologically nontrivial orbits encircling their Dirac node(s). [ABSTRACT FROM AUTHOR]

The electronic structure of semimetallic transition-metal dichalcogenides, such as WTe 2 and orthorhombic γ - MoTe2, are claimed to contain pairs of Weyl points or linearly touching electron and hole pockets associated with a nontrivial Chern number. For this reason, these compounds were recently claimed to conform to a new class, deemed type-II, of Weyl semimetallic systems. A series of angle-resolved photoemission experiments (ARPES) claim a broad agreement with these predictions detecting, for example, Fermi arcs at the surface of these crystals. We synthesized single crystals of semimetallic MoTe2 through a Te flux method to validate these predictions through measurements of its bulk Fermi surface (FS) via quantum oscillatory phenomena. We find that the superconducting transition temperature of γ - MoTe2 depends on disorder as quantified by the ratio between the room- and low-temperature resistivities, suggesting the possibility of an unconventional superconducting pairing symmetry. Similarly to WTe2, the magnetoresistivity of γ - MoTe2 does not saturate at high magnetic fields and can easily surpass 106%. Remarkably, the analysis of the de Haas-van Alphen (dHvA) signal superimposed onto the magnetic torque indicates that the geometry of its FS is markedly distinct from the calculated one. The dHvA signal also reveals that the FS is affected by the Zeeman effect precluding the extraction of the Berry phase. A direct comparison between the previous ARPES studies and density-functional-theory (DFT) calculations reveals a disagreement in the position of the valence bands relative to the Fermi level ɛF. Here, we show that a shift of the DFT valence bands relative to ɛF, in order to match the ARPES observations, and of the DFT electron bands to explain some of the observed dHvA frequencies, leads to a good agreement between the calculations and the angular dependence of the FS cross-sectional areas observed experimentally. However, this relative displacement between electron and hole bands eliminates their crossings and, therefore, the Weyl type-II points predicted for γ - MoTe2. [ABSTRACT FROM AUTHOR]

Weyl type-II fermions are massless quasiparticles that obey the Weyl equation and which are predicted to occur at the boundary between electron and hole pockets in certain semimetals, i.e., the (W,Mo)(Te,P)2 compounds. Here, we present a study of the Fermi surface of WP2 via the Shubnikov-de Haas (SdH) effect. Compared to other semimetals, WP2 exhibits a very low residual resistivity, i.e., ρ0≃10nΩcm, which leads to perhaps the largest nonsaturating magnetoresistivity [ρ(H)] reported for any compound. For the samples displaying the smallest ρ0,ρ(H) is observed to increase by a factor of 2.5×107% under μ0H=35 T at T=0.35 K. The angular dependence of the SdH frequencies is found to be in excellent agreement with the first-principles calculations when the electron and hole bands are shifted by 30 meV with respect to the Fermi level. This small discrepancy could have implications for the predicted topological character of this compound. [ABSTRACT FROM AUTHOR]