Nodal-sphere semimetals (NSSMs), featuring spherical band degeneracies in momentum space, constitute a fascinating class of topological materials. However, their realization in real materials is severely hampered by discrete crystallographic symmetry constraints, often resulting in gapped “pseudo” nodal spheres. Here, combining first-principles calculations and symmetry analysis, we predict a new three-dimensional boron allotrope, ${\text{CT-B}}_{24}$, as a nearly ideal NSSM. Its structural stability is systematically confirmed by phonon calculations, ab initio molecular dynamics simulations at 600 K, and elastic constant analysis. Notably, the electronic structure of ${\text{CT-B}}_{24}$ exhibits two bands crossing linearly near the Fermi level, forming a quasinodal sphere around the $\mathrm{\Gamma }$ point. The maximum energy gap is merely 0.008 meV, which is two orders of magnitude smaller than the gaps reported in previous pseudo-NSSMs. Furthermore, the (001) surface hosts pronounced drumheadlike surface states located outside the projected nodal sphere, providing distinct signatures detectable by angle-resolved photoemission spectroscopy. The nodal sphere also demonstrates remarkable robustness and tunability under external strain, driving a topological phase transition from an NSSM to a critical transition state and finally to a trivial insulator. Our work not only presents a superior material platform for exploring nodal-sphere physics but also suggests potential for strain-tunable topological devices.

Close

PrevNext

View figure in article

• Symmetry protected topological states
• Topological phase transition
• Topological materials
• First-principles calculations