Browsing by Author "Appelt, Wilhelm H."

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    Predicting the conductance of strongly correlated molecules: the Kondo effect in perchlorotriphenylmethyl/Au junctions
    Appelt, Wilhelm H.; Droghetti, Andrea; Chioncel, Liviu; Radonjić, Miloš; Muñoz, Enrique T.; Kirchner, Stefan; Vollhardt, Dieter; Rungger, Ivan
    Stable organic radicals integrated into molecular junctions represent a practical realization of the single-orbital Anderson impurity model. Motivated by recent experiments for perchlorotriphenylmethyl (PTM) molecules contacted to gold electrodes, we develop a method that combines density functional theory (DFT), quantum transport theory, numerical renormalization group (NRG) calculations and renormalized super-perturbation theory (rSPT) to compute both equilibrium and non-equilibrium properties of strongly correlated nanoscale systems at low temperatures effectively from first principles. We determine the possible atomic structures of the interfaces between the molecule and the electrodes, which allow us to estimate the Kondo temperature and the characteristic transport properties, which compare well with experiments. By using the non-equilibrium rSPT results we assess the range of validity of equilibrium DFT + NRG-based transmission calculations for the evaluation of the finite voltage conductance. The results demonstrate that our method can provide qualitative insights into the properties of molecular junctions when the molecule-metal contacts are amorphous or generally ill-defined, and that it can further give a fully quantitative description when the experimental contact structures are well characterized.
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    Superconducting nature of the Bi-II phase of elemental bismuth
    Khasanov, Rustem; Radonjić, Miloš; Luetkens, Hubertus; Morenzoni, Elvezio; Simutis, Gediminas; Schönecker, Stephan; Appelt, Wilhelm H.; Östlin, Andreas; Chioncel, Liviu; Amato, Alex
    The superconductivity in the Bi-II phase of elemental bismuth (transition temperature Tc≃3.92 K at pressure p≃2.80 GPa) was studied experimentally by means of the muon-spin rotation as well as theoretically by using the Eliashberg theory in combination with density functional theory calculations. Experiments reveal that Bi-II is a type-I superconductor with a zero temperature value of the thermodynamic critical field Bc(0)≃31.97 mT. The Eliashberg theory approach provides a good agreement with the experimental Tc and the temperature evolution of Bc. The estimated value for the retardation (coupling) parameter kBTc/ωln≈0.07 (ωln is the logarithmically averaged phonon frequency) suggests that Bi-II is an intermediately coupled superconductor.