Strain-Induced Ideal Topological Semimetal in Ort-B-32 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-B-32," 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 k z = 0 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 x 10(6) 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.