Predicted superconductivity of Ni2VAl and pressure dependence of superconductivity in Ni2NbX (X  =  Al, Ga and Sn) and Ni2VAl

Reddy, P V S and V, Kanchana and G, Vaitheeswaran and Singh, D J (2016) Predicted superconductivity of Ni2VAl and pressure dependence of superconductivity in Ni2NbX (X  =  Al, Ga and Sn) and Ni2VAl. Journal of Physics Condensed Matter, 28. pp. 115703-1. ISSN 0953-8984

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A first-principles study of the electronic and superconducting properties of the Ni2VAl Heusler compound is presented. The electron–phonon coupling constant of ${{\lambda}_{\text{ep}}}=0.68$ is obtained, which leads to a superconducting transition temperature of ${{T}_{\text{c}}}=\sim 4$ K (assuming a Coulomb pseudopotential ${{\mu}^{\ast}}=0.13$ ), which is a relatively high transition temperature for Ni based Heusler alloys. The electronic density of states reveals a significant hybridization between Ni-eg and V-t 2g states around the Fermi level. The Fermi surface, consisting of two electron pockets around the X-points of the Brillouin zone, exhibits nesting and leads to a Kohn anomaly of the phonon dispersion relation for the transverse acoustic mode TA2 along the (1, 1, 0) direction, which is furthermore found to soften with pressure. As a consequence, ${{T}_{\text{c}}}$ and ${{\lambda}_{\text{ep}}}$ vary non-monotonically under pressure. The calculations are compared to similar calculations performed for the Ni2NbX (X  =  Al, Ga and Sn) Heusler alloys, which experimentally have been identified as superconductors. The experimental trend in ${{T}_{\text{c}}}$ is well reproduced, and reasonable quantitative agreement is obtained. The calculated ${{T}_{\text{c}}}$ of Ni2VAl is larger than either calculated or observed ${{T}_{\text{c}}}$ s of any of the Nb compounds. The Fermi surfaces of Ni2NbAl and Ni2NbGa consist of only a single electron pocket around the X point, however under compression a second electron pocket similar to that of Ni2VAl emerges Ni2NbAl and the ${{T}_{\text{c}}}$ increases non-monotonically in all the compounds. Fermi surface nesting and associated Kohn anomalies are a common feature of all four compounds, albeit weakest in Ni2VAl.

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Item Type: Article
Additional Information: PVSR would also like to acknowledge IIT-Hyderabad for providing computational facilities. GV would like to acknowledge CMSD-University of Hyderabad for providing computational facilities. VK and GV would like to acknowledge A Svane and N E Christensen for fruitful discussions during the beginning of this project.
Uncontrolled Keywords: Fermi surface nesting, charge density wave, Kohn anomaly, superconductivity, pressure effect on superconductivity
Subjects: Physics
Divisions: Department of Physics
Depositing User: Team Library
Date Deposited: 01 Mar 2016 09:16
Last Modified: 22 Jun 2018 04:29
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