Strain‐Induced Ideal Topological Semimetal in Ort‐B₃₂ Holding Parallel Arc‐Like Nodal Lines and Anisotropic Multiple Weyl Fermions

Ideal topological semimetals, which are composed of nontoxic lightweight elements and host clean Dirac/Weyl fermions near Fermi energy without contamination from other quasiparticles, are highly desirable for experimental detection and practical application. Herein, using first‐principles calculations, it is demonstrated that a new stable boron allotrope, termed “ort‐B₃₂,” harbors the needed clean Weyl fermions in a sizable energy window under modest tensile strain. Due to the protection of mirror symmetry, the band crossings form two pairs of parallel arc‐like nodal lines, running across the whole Brillouin zone in the plane. The topological features of these nodal lines are characterized by the drumhead‐like surface state and nonzero topological invariant. Remarkably, the examination of slope index reveals that the type‐I, type‐II, and type‐III Weyl states can be found in different moment directions with the value of Fermi velocities ranging from 0 to 1.15 × 10⁶ m s⁻¹. These results not only establish a striking new boron allotrope, but also highlight a promising mechanically induced method for obtaining ideal Weyl semimetal.