Dirac cone protected by non symmorphic symmetry and three dimensional Dirac line node in ZrSiS

Materials harbouring exotic quasiparticles, such as massless Dirac and Weyl fermions, have garnered much attention from physics and material science communities due to their exceptional physical properties such as ultra high mobility and extremely large magnetoresistances. Here, we show that the highly stable, non toxic and earth abundant material, ZrSiS, has an electronic band structure that hosts several Dirac cones that form a Fermi surface with a diamond shaped line of Dirac nodes. We also show that the square Si lattice in ZrSiS is an excellent template for realizing new types of two dimensional Dirac cones recently predicted by Young and Kane. Finally, we find that the energy range of the linearly dispersed bands is as high as 2 amp; 8201;eV above and below the Fermi level; much larger than of other known Dirac materials. This makes ZrSiS a very promising candidate to study Dirac electrons, as well as the properties of lines of Dirac node

Single Skyrmion Generation via a Vertical Nanocontact in a 2D Magnet Based Heterostructure

Skyrmions have been well studied in chiral magnets and magnetic thin films due to their potential application in practical devices. Recently, monochiral skyrmions have been observed in two dimensional van der Waals magnets. Their atomically flat surfaces and capability to be stacked into heterostructures offer new prospects for skyrmion applications. However, the controlled local nucleation of skyrmions within these materials has yet to be realized. Here, we utilize real space X ray microscopy to investigate a heterostructure composed of the 2D ferromagnet Fe3GeTe2 FGT , an insulating hexagonal boron nitride layer, and a graphite top electrode. Upon a stepwise increase of the voltage applied between the graphite and FGT, a vertically conducting pathway can be formed. This nanocontact allows the tunable creation of individual skyrmions via single nanosecond pulses of low current density. Furthermore, time resolved magnetic imaging highlights the stability of the nanocontact, while our micromagnetic simulations reproduce the observed skyrmion nucleation proces

On Surface Polymerization of 1,6 Dibromo 3,8 diiodpyrene A Comparative Study on Au 111 Versus Ag 111 by STM, XPS, and NEXAFS

The surface chemistry of 1,6-dibromo-3,8-diiodopyrene (Br₂I₂Py) is comparatively studied on Au(111) versus Ag(111) surfaces under ultrahigh vacuum conditions by a combination of high-resolution scanning tunneling microscopy (STM) and X-ray spectroscopy. The chemical state of the molecular networks, that is, the dehalogenation and the possible formation of organometallic intermediates, is assessed by X-ray photoelectron spectroscopy. In addition, pyrene tilt angles are quantified by carbon K-edge near edge X-ray absorption fine structure experiments. Upon room-temperature (RT) deposition of Br₂I₂Py onto Au(111), only partial deiodination was found, and STM revealed the coexistence of ordered arrangements of both intact Br₂I₂Py molecules and organometallic dimers as well as few larger aggregates. Further annealing to 100 °C triggered full deiodination followed by the formation of organometallic chains of otherwise still brominated molecules. By contrast, on Ag(111), iodine is fully and bromine is partly dissociated upon RT deposition of Br₂I₂Py. The initially disordered organometallic aggregates can be reorganized into more ordered structures by mild annealing at 125 °C. Yet, the conversion of the organometallic intermediates into well-defined cross-linked quasi 2D covalent networks was neither possible on Au(111) nor on Ag(111). This is attributed to the large steric hindrance in the covalently linked adsorbed state