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 axis due to accidental degeneracies of two bands corresponding to different 2-dimensional irreducible representations of the C_6v group. The surface states have two midgap bands emanating from the projection of the bulk Dirac points, in accordance with nontrivial Zak phases for each glide sector. 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 including nonmagnetic linked-nodal-line and Weyl semimetals as well as ferromagnetic Weyl semimetals.