Abstract
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.
Highlights
The field of superconductivity in Materials Science has evolved enormously, from conventional to unconventional passing through the ill-defined undetermined category [1]
To validate the simulations the PDF of the resulting amorphous structure is directly compared with the experimental curve; the computational results for the amorphous bismuth (a-Bi) structure are shown in Fig 1A which reveals an exceptional agreement with the experimental PDF
We report the computer generation of amorphous bismuth that displays pair distribution functions for a 216-atom supercell in agreement with experiment
Summary
The field of superconductivity in Materials Science has evolved enormously, from conventional to unconventional passing through the ill-defined undetermined category [1]. Superconductivity of amorphous bismuth (a-Bi), considered conventional, was discovered several decades ago with a critical transition temperature of Tc * 6 K, whereas its crystalline counterpart (x-Bi) has not been found yet to superconduct, at least above 10−2 K [2] This put the subject in the foreground decades ago, but it faded into the background as it was not possible to understand the dichotomy observed in the two phases. For this reason bismuth is an interesting material for studying the influence of the structure-property relations on superconductivity. Studying the electronic and vibrational properties of these two bismuth phases may contribute to disentangle the PLOS ONE | DOI:10.1371/journal.pone.0147645 January 27, 2016
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