The noncentrosymmetric NbReSi superconductor with Tc≃6.5 K is characterized by the relatively large upper critical magnetic field. Its multigap features were observed experimentally. Recent studies suggested the realization of P6¯2m or Ima2 symmetry. We discuss the dynamical properties of both symmetries (e.g., phonon spectra). In this paper, using the ab initio techniques, we clarify this ambiguity, and conclude that the Ima2 symmetry is unstable, and P6¯2m should be realized. The P6¯2m symmetry is also stable in the presence of external hydrostatic pressure. We show that NbReSi with the P6¯2m symmetry should host phonon surface states for (100) and (110) surfaces. Additionally, we discuss the main electronic properties of the system with the stable symmetry.

Ternary compound YAlSi crystallizes with orthorhombic Cmcm symmetry. This structure contains Y–Si pairs of atoms, creating honeycomb-like sublattices. In this paper, we investigate the dynamical properties of the system, focusing on the chiral modes. These modes are associated with the circular motion of the atoms. We show that the chiral modes can be realized in the YAlSi compound, and it makes this compound suitable for further experimental study of the chiral phonons.

Recently, superconductivity was discovered in the infinite layer of hole-doped nickelates NdNiO2. Contrary to this, superconductivity in LaNiO2 is still under debate. This indicates the crucial role played by the f electrons on the electronic structure and the pairing mechanism of infinite-layer nickelates. Here, we discuss the role of the electron correlations in the f electron states and their influence on the electronic structure. We show that the lattice parameters are in good agreement with the experimental values, independent of the chosen parameters within the DFT+U approach. Increasing Coulomb interaction U tends to shift the f states away from the Fermi level. Surprisingly, independently of the position of f states with respect to the Fermi energy, these states play an important role in the electronic band structure, which can be reflected in the modification of the NdNiO2 effective models.

No abstract

No abstract