Possible superconductivity in Bismuth (111) bilayers. Their electronic and vibrational properties from first principles
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.119
Possible superconductivity in Bismuth (111) bilayers. Their electronic and vibrational properties from first principles David Hinojosa-Romero1, Isaías Rodriguez2, Alexander Valladares2, Renela M. Valladares2 and Ariel A. Valladares1 *. 1
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, Ciudad Universitaria, CDMX, 04510, México. 2 Facultad de Ciencias, Universidad Nacional Autónoma de México, Apartado Postal 70-542, Ciudad Universitaria, CDMX, 04510, México
* Corresponding Author: Ariel A. Valladares, [email protected]
ABSTRACT
Using a 72-atom supercell we report ab initio calculations of the electronic and vibrational densities of states for the bismuth (111) bilayers (bismuthene) with periodic boundary conditions and a vacuum of 5 Å, 10 Å and 20 Å. We find that the electronic density of states shows a metallic character at the Fermi level and that the vibrational density of states manifests the expected gap due to the layers. Our results indicate that a vacuum down to 5 Å does not affect the electronic and vibrational structures noticeably. A comparison of present results with those obtained for the Wyckoff structure is displayed. Assuming that the Cooper pairing potential is similar for all phases and structures of bismuth, an estimate of the superconducting transition temperature gives 2.61 K for the bismuth bilayers.
INTRODUCTION Bulk bismuth is known to be a semimetal, a metal or a superconductor, with peculiar electronic and vibrational properties depending on whether it is crystalline or amorphous or depending on the pressure applied on it. At ambient pressure and temperature, it crystallizes in the Wyckoff structure, Bi-I, [1] with rhombohedral symmetry in which each atom has three equidistant nearest-neighbor atoms and three equidistant next-nearest neighbors slightly further away, resulting in a buckled 2D honeycomb bilayer lying perpendicular to the [111] crystallographic direction. Bismuthene, or the bilayers (111) of bismuth, Bi (111), recently has been the subject of much interest and investigation as an example of non-carbon low-dimensional materials and the influence of this low dimensionality on its electronic and transport properties. It has been argued that in this layered form, bismuth has properties of topological insulators [2-4] which are bulk insulators with protected boundary states [5]. This state of matter appears when there is an inversion in the electronic bands of 2D materials caused by perturbations [6]. Among the perturbing agents the following are
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cited: strains in the systems, controlled quantum well width in the process of growth, doping [6, 7] and recently, for the Bi (111), the strength of the spin-orb
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