Ab initio Study of the Amorphous Cu-Bi System
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MRS Advances Β© 2019 Materials Research Society DOI: 10.1557/adv.2019.83
Ab initio Study of the Amorphous Cu-Bi System D. Hinojosa-Romero1, I. Rodriguez2, A. Valladares2, R. M. Valladares2, A. A. Valladares1* 1 Condensed Matter Department, Instituto de Investigaciones en Materiales, UNAM.
2 Physics Department, Facultad de Ciencias, UNAM.
* Corresponding Author: Ariel A. Valladares, [email protected]
ABSTRACT
As a pure element, bismuth is a semimetal which possesses several interesting physical properties, not all of them well understood. The recent discovery of superconductivity, as predicted by our group, and the increasing superconducting transition temperature as the pressure applied increases, are some examples of its particularities. Also, the fact that the amorphous phase is superconductive with a transition temperature several orders of magnitude larger than the crystalline at ambient pressure is unusual. These phenomena have also motivated our predictions for the transition temperatures of Bi-bilayers and the Bi-IV phase. When mixed with other elements, bismuth seems to contribute to the superconducting character of the resulting material. Here we study the binary copper-bismuth amorphous system which is known to superconduct in diverse compositions. Using ab initio molecular dynamics and the undermelt-quench method, we generate an amorphous structure for a 144-atom supercell corresponding to the Cu61Bi39 system. We calculate the electronic and vibrational densities of states for the amorphous system and estimate a superconducting critical temperature of 4.2 K for the amorphous state.
INTRODUCTION Superconductivity, a phenomenon in which an electrical current can flow through a material with no resistance, has been an appealing field of study since its discovery on mercury, tin and lead by H. Kamerlingh Onnes in 1911 [1]. Later in 1957, J. Bardeen, L. Cooper and J. R. Schrieffer [2] proposed a microscopic theory of superconductivity based on the coupled movement of electrons through the material, leading also to a correct
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description of the Meissner effect that is present in superconducting materials and the critical temperature Tc below which this phenomenon takes place. Along the years, several theories explaining the superconducting behavior of solids have emerged, each one proposing different mechanisms in which the pairing of electrons occur. However, the successful predictions of the BCS theory remain up to present time. According to the BCS theory, the fundamental properties that determine the Tc for a particular solid are the density of electronic states at the Fermi level, N(EF), the Debye temperature, ΞΈD, and the so-called electron-phonon coupling represented through the interaction potential V0. This is expressed in the equation: ππ = 1.13 ππ· πxp(β1/π(πΈπΉ)
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