We show by angle-resolved photoemission spectroscopy that a tunable gap in quasi-free-standing monolayer graphene on Au can be induced by hydrogenation. The size of the gap can be controlled via hydrogen loading and reaches approximately 1.0 eV for a hydrogen coverage of 8%. The local rehybridization from sp(2) to sp(3) in the chemical bonding is observed by X-ray photoelectron spectroscopy and X-ray absorption and allows for a determination of the amount of chemisorbed hydrogen. The hydrogen induced gap formation is completely reversible by annealing without damaging the graphene. Calculations of the hydrogen loading dependent core level binding energies and the spectral function of graphene are in excellent agreement with photoemission experiments. Hydrogenation of graphene gives access to tunable electronic and optical properties and thereby provides a model system to study hydrogen storage in carbon materials.

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We derive a nonlinear differential equation for the gap parameter of a superfluid Fermi system by performing a suitable coarse graining of the Bogoliubov-de Gennes (BdG) equations throughout the BCS-BEC crossover, with the aim of replacing the time-consuming solution of the original BdG equations by the simpler solution of this novel equation. We perform a favorable numerical test on the validity of this new equation over most of the temperature-coupling phase diagram, by an explicit comparison with the full solution of the original BdG equations for an isolated vortex. We also show that the new equation reduces both to the Ginzburg-Landau equation for Cooper pairs in weak coupling close to the critical temperature and to the Gross-Pitaevskii equation for composite bosons in strong coupling at low temperature.

The temperature dependence of an isolated quantum vortex, embedded in an otherwise homogeneous fermionic superfluid of infinite extent, is determined via the Bogoliubov–de Gennes (BdG) equations across the BCS-BEC crossover. Emphasis is given to the BCS side of this crossover, where it is physically relevant to extend this study up to the critical temperature for the loss of the superfluid phase, such that the size of the vortex increases without bound. To this end, two techniques are introduced. The first one solves the BdG equations with “free boundary conditions,” which allows one to determine with high accuracy how the vortex profile matches its asymptotic value at a large distance from the center, thus avoiding a common practice of constraining the vortex in a cylinder with infinite walls. The second one improves on the regularization procedure of the self-consistent gap equation when the interparticle interaction is of the contact type, and permits us to considerably reduce the time needed for its numerical integration by drawing elements from the derivation of the Gross-Pitaevskii equation for composite bosons starting from the BdG equations

The effective use of swift ion beams in cancer treatment (known as hadrontherapy) as well as appropriate protection in manned space missions rely on the accurate understanding of the energy delivery to cells that damages their genetic information. The key ingredient characterizing the response of a medium to the perturbation induced by charged particles is its electronic excitation spectrum. By using linear-response time-dependent density functional theory, we obtained the energy and momentum transfer excitation spectrum (the energy-loss function, ELF) of liquid water (the main constituent of biological tissues), which was in excellent agreement with experimental data. The inelastic scattering cross sections obtained from this ELF, together with the elastic scattering cross sections derived by considering the condensed phase nature of the medium, were used to perform accurate Monte Carlo simulations of the energy deposited by swift carbon ions in liquid water and carried away by the generated secondary electrons, producing inelastic events such as ionization, excitation, and dissociative electron attachment (DEA). The latter are strongly correlated with cellular death, which is scored in sensitive volumes with the size of two DNA convolutions. The sizes of the clusters of damaging events for a wide range of carbon-ion energies, from those relevant to hadrontherapy up to those for cosmic radiation, predict with unprecedented statistical accuracy the nature and relative magnitude of the main inelastic processes contributing to radiation biodamage, confirming that ionization accounts for the vast majority of complex damage. DEA, typically regarded as a very relevant biodamage mechanism, surprisingly plays a minor role in carbon-ion induced clusters of harmful events.

Abstract. -With reference to the broad and narrow Fano-Feshbach resonances of 6 Li at about 822G and 543G, we show that for the broad resonance a molecular coupled-channel calculation can be mapped with excellent accuracy onto an effective single-channel problem with a contact interaction. This occurs for a wide enough range of the magnetic field, that the full BCS-BEC crossover can be realized with a typical trap. For the narrow resonance, the mapping onto a single-channel problem and the realization of the BCS-BEC crossover are restricted to too narrow a range of the magnetic field to obtain them in practice. A general criterion is also formulated for deciding whether the BCS-BEC crossover can be exhausted within the single-channel model for any specific Fano-Feshbach resonance. In this way, the BCS-BEC crossover for Fermi atoms with the broad resonance is placed on the same footing as the corresponding crossover for different physical systems. In this context, a large amount of work has been made by adopting a contact potential for the effective fermion-fermion attraction, regularized in terms of the scattering length a F [12][13][14]. The use of this potential considerably simplifies the many-body diagrammatic structure, both in the normal [13,14] and broken-symmetry [13,15] phases. By this approach, only fermionic degrees of freedom are retained in the many-body Hamiltonian, in the same spirit of the original BCS theory [16]. Since just the quantity a F is varied in a controlled way by sweeping the magnetic field across a FF resonance, it would appear that trapped Fermi gases constitute an ideal testing ground for many-body theories based on the above two-body interaction. Previous theoretical work using the same interaction could thus be adapted to trapped Fermi gases with limited effort.The use of the same effective two-body interaction for such different systems like hightemperature superconductors and trapped Fermi gases may also lead to the emergence of universal features. This should be especially desirable, as the insights gleaned from the c EDP Sciences

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The enrichment of Li in the Universe is still unexplained, presenting various puzzles to astrophysics. One open issue is that of obtaining reliable estimates for the rate of e − -captures on 7 Be, for T and ρ conditions different from the solar ones. This is of crucial importance to model the Galactic nucleosynthesis of Li. In this framework, we present here a new theoretical method for calculating the e − -capture rate in conditions typical of evolved stars. Furthermore, we show how our approach compares with state-of-the-art techniques for solar conditions, where various estimates are available. Our computations include: i) "traditional" calculations of the electronic density at the nucleus, to which the e − -capture rate for 7 Be is proportional, for different theoretical approaches including the Thomas-Fermi, Poisson-Boltzmann and Debye-Hückel (DH) models of screening, ii) a new computation, based on a formalism that goes beyond the previous ones, adopting a mean-field "adiabatic" approximation to the scattering process. The results obtained with the new approach as well as with the traditional ones and their differences are discussed in some detail, starting from solar conditions, where our approach and the DH model essentially converge to the same solution. We then analyze the applicability of both our method and the DH model to a rather broad range of T and ρ values, embracing those typical of red giant stars, where both bound and continuum states contribute to the capture. We find that, over a wide region of the parameter space explored, the DH approximation does not really stand, so that the more general method we suggest should be preferred. As a first application, we briefly reanalyze the 7 Li abundances in RGB and AGB stars of the Galactic Disk in the light of a revision in the Be-decay only; we however underline that the changes we find in the electron density at the nucleus would induce effects also on the electron screening (for p-captures on Li itself, as well as for other nuclei) so that our new approach might have rather wide astrophysical consequences.