Electron-Phonon Interaction and Superconductivity in Hexagonal Ternary Carbides Nb2AC (A: Al, S, Ge, As and Sn)

Ertugrul Karaca, Peter John Phares Byrne, Philip James Hasnip, Huseyin Tutuncu, Matt Probert

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The superconducting transition temperatures Tc of hexagonal Nb2AC (A: Al, S, Ge, As and Sn) are investigated using density functional perturbation theory to model the electron-phonon interaction. A critical assessment of the calculated electronic structure and density of states revealed that the electronic states near to the Fermi level are mostly composed of the Nb 4d states, which are responsible for the electrical conductivity. The theoretical Tc data from electron-phonon calculations are in excellent agreement with the Fr ̈ohlich model, and this model was used as a computationally efficient screening method to identify promising Nb-C M2AX phase materials. For Nb2AC (A: Zn,Cd, Al, Ga, In, Tl, Si, Pb and P), the model indicated that Nb2AlC should have the highest Tc of this set, a little lower than Nb2GeC and comparable to Nb2SC and Nb2SnC. Nb2AlC has not been studied experimentally, but this result was confirmed by full electron-phonon calculations, which also revealed that the mechanism for superconductivity is the interactions of Nb 4d-state electrons with low-frequency phonons (in particular, acoustic phonon and low–frequency optical phonons dominated by Nb and the A element). The average electron-phonon coupling parameter was found to be λ∼0.646, 0.739, 0.685, 0.440 and 0.614 for Nb2AC (A: Al, S, Ge, As and Sn), respectively, with a corresponding superconducting critical temperature Tc∼6.7 K, 7.7 K, 9.8 K, 2.1 K and 6.3 K, respectively.
Original languageEnglish
Article number045001
JournalElectronic Structure
Issue number4
Publication statusPublished - 22 Oct 2021

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