About the ground state structure and superconductivity of the SrAlGe compound

• Published in: Physica. C, Superconductivity Superconductivity, 2021-05, Vol.584, p.1353868, Article 1353868
• Main Authors: Djelloul, M., Bouderba, H., Beddiaf, R., Bentria, B., Helifa, B.
• Format: Article
• Language: English
• Subjects: ab-initio calculations; BCS theory; Coupling; Crystal structure; Density; Density functional theory; Electronic structure; Germanides; MgB2; Phase stability; Phonon; Phonons; Scanning electron microscopy; SrAlGe; Structural stability; Studies; Superconductivity; Superconductors; Unit cell
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2021.1353868

•The AlB2-like structure is shown to be dynamically unstable for the SrAlGe compound.•A new dynamically stable strucural model with a doubled unit cell is proposed.•The correlation between electronic structure and dynamical stability is explored.•A peierls like distorsion is shown to primarly affect the Al−pz orbitals.•A puckring mode is shown to have the main contribution in the superconducting coupling mechanism. In the present investigation, based on density functional theory computational approach, we show how the experimentally accepted AlB2-like structure of the SrAlGe compound is suggested to be dynamically unstable at 0 K. We propose a stable configuration that is deduced from the detailed analysis of the phonon spectrum with a doubled unit cell and buckled AlGe layers. It allows to closely reproduce the experimental critical superconducting temperature assuming a phonon mediated superconductivity as described within BCS theory. A soft puckering mode is identified both as the cause for the structural instability and as the main contributor in the electron-phonon coupling constant. From the detailed study of the electronic structure, we show how a peierls-like distortion with the crystal symmetry lowering, affecting mainly the Al-pz orbitals, is correlated with the puckering and with the electron-phonon coupling mechanism.