To investigate the relationship between atomic topology, vibrational and electronic properties and superconductivity of bismuth, a 216-atom amorphous structure (a-Bi216) was computer-generated using our undermelt-quench approach. Its pair distribution function compares well with experiment. The calculated electronic and vibrational densities of states (eDOS and vDOS, respectively) show that the amorphous eDOS is about 4 times the crystalline at the Fermi energy, whereas for the vDOS the energy range of the amorphous is roughly the same as the crystalline but the shapes are quite different. A simple BCS estimate of the possible crystalline superconducting transition temperature gives an upper limit of 1.3 mK. The e-ph coupling is more preponderant in a-Bi than in crystalline bismuth (x-Bi) as indicated by the λ obtained via McMillan’s formula, λc = 0.24 and experiment λa = 2.46. Therefore with respect to x-Bi, superconductivity in a-Bi is enhanced by the higher values of λ and of eDOS at the Fermi energy.

We use zero-and longitudinal-field muon spin rotation and relaxation to study the muon states in the organic molecular ferromagnet: j3-phase para-nitrophenyl nitronyl nitroxide (p-NPNN). Below Tc = 0.65 K, oscillations in the relaxation function are observed in zero applied field which follow the magnetic order parameter, implying that the muon is bonded in an electronic spin-singlet state. We also study the behaviour of the oscillations in an applied longitudinal field and interpret the results by considering the magnetisation process and the demagnetising field. A significant field-induced repolarisation is also observed which is ascribed to the presence of spin-triplet states formed by a fraction of muons.Recently, there has been much interest in the search for a purely organic molecular ferromagnet which contains only light elements (like carbon, nitrogen, hydrogen, and oxygen) [l]. The frst such material to be found, the j3 crystal phase of para-nitrophenyl nitronyl nitroxide (p-NPNN, see fig. lb)), was reported to have a Curie temperature (T,) of 0.60K, a discovery which was made using heat capacity and magnetisation measurements [2,3]. The unpaired spin in this nitronyl nitroxide is associated with the N-0 groups. The role of the rest of the molecule is to ensure the appropriate overlap of the correct orbitals on neighbouring molecules to produce 3D ferromagnetism. A whole series of materials which incorporate this nitronyl nitroxide group are currently being synthesized in order to provide a systematic study of the effects of the variation of the rest of the molecule on the molecular packing and overlap and hence on the magnetic properties.Zero-field (ZF) muon spin rotation/relaxation (pSR) studies on aligned single crystals [4]and polycrystalline [51 samples have also demonstrated magnetic order with Tc -0.65 K; in these experiments, the muon spin precession rate directly yields the value of the internal magnetic field at the muon site. In a pSR experiment, a beam of spin-polarized muons is stopped in a target specimen. Each muon subsequently decays (with a mean lifetime of z p = = 2.2 ps), emitting a positron preferentially along the muon spin direction because of the parity violation of the weak interaction [6]. The time histograms N * (t) of positrons counted in the 8 Les Editions de Physique

Magnetism in palladium has been the subject of much work and speculation. Bulk crystalline palladium is paramagnetic with a high magnetic susceptibility. Palladium under pressure and palladium nanoclusters have generated interest to scrutinize its magnetic properties. Here we report another possibility: Palladium may become an itinerant ferromagnet in the amorphous bulk phase at atmospheric pressure. Atomic palladium is a d 10 element, whereas bulk crystalline Pd is a d 10−x (sp) x material; this, together with the possible presence of unsaturated bonds in amorphous materials, may explain the remnant magnetism reported herein. This work presents and discusses magnetic effects in bulk amorphous palladium.

A thermal procedure and an ab initio molecular-dynamics method based on the Harris functional, applied to originally crystalline, periodically continued 64-atom cubic cells, is used to generate random networks of four different materials of varying degrees of covalency: C, Si, Ge, and a nearly stoichiometric sample of Si-N. We obtain their radial distribution functions ͑RDF's͒ for four different time steps, one for each material, using densities dictated by experiment. The simulated RDF's for amorphous C, Si, and Ge show the four characteristic radial peaks observed experimentally. For the nearly stoichiometric SiN 1.29 sample two runs were performed and averaged. The agreement between simulated and experimental RDF's is very good.

The first successful theory of superconductivity was the one proposed by Bardeen, Cooper and Schrieffer in 1957. This breakthrough fostered a remarkable growth of the field that propitiated progress and questionings, generating alternative theories to explain specific phenomena. For example, it has been argued that Bismuth, being a semimetal with a low number of carriers, does not comply with the basic hypotheses underlying BCS and therefore a different approach should be considered. Nevertheless, in 2016 based on BCS we put forth a prediction that Bi at ambient pressure becomes a superconductor at 1.3 mK. A year later an experimental group corroborated that in fact Bi is a superconductor with a transition temperature of 0.53 mK, a result that eluded previous work. So, since Bi is superconductive in almost all the different structures and phases, the question is why Bi-IV has been elusive and has not been found yet to superconduct? Here we present a study of the electronic and vibrational properties of Bi-IV and infer its possible superconductivity using a BCS approach. We predict that if the Bi-IV phase structure were cooled down to liquid helium temperatures it would also superconduct at a Tc of 4.25 K.

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Carbon and silicon have been consistently proposed as elements useful in the generation of porous materials. Carbon has been insistently postulated as a promising material to store hydrogen, and crystalline silicogermanate zeolites have recently been synthesized and are being considered in catalytic processes. In the present work we report an approach to generating porous materials, in particular porous carbon and silicon, which leads to the existence of nanopores within the bulk. The method consists in constructing a crystalline diamond-like supercell with 216 atoms with a density (volume) close to the real value, then halving the density by doubling the volume (50% porosity), and subjecting the resulting supercell to an ab initio molecular dynamics process at 300 K for Si, and 1000 K for carbon, followed by geometry relaxation. The resulting samples are essentially amorphous and display pores along some of the "crystallographic" directions. We report their radial distribution functions and the pore structure where prominent.

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