Ideal spin-orbit-free Dirac semimetal and diverse topological transitions in Y8CoIn3 family

Topological semimetals, known for their intriguing properties arising from band degeneracies, have garnered significant attention. However, the discovery of a material realization and the detailed characterization of spinless Dirac semimetals have not yet been accomplished. Here, we propose from first-principles calculations that the RE8CoX3 group (RE = rare earth elements, X = Al, Ga, or In) contains ideal spinless Dirac semimetals whose Fermi surfaces are fourfold degenerate band-crossing points (without including spin degeneracy). Despite the lack of space inversion symmetry in these materials, Dirac points are formed on the rotation-symmetry axis due to accidental degeneracies of two bands corresponding to different 2-dimensional irreducible representations of the C6v group. We also investigate, through first-principles calculations and effective model analysis, various phase transitions caused by lattice distortion or elemental substitutions from the Dirac semimetal phase to distinct topological semimetallic phases such as nonmagnetic linked-nodal-line and Weyl semimetals (characterized by the second Stiefel–Whitney class) and ferromagnetic Weyl semimetals. Band degeneracies at the Fermi level in topological semimetals are sources of intriguing interference effects between electronic states around the degeneracy points. Here, the RE8CoX3 compounds, with RE = rare-earth and X = Al, Ga, or In, are proposed as realizations of ideal spinless Dirac semimetals hosting the fourfold degenerate band-crossing points without the spin degrees of freedom.