The interplay between light and matter attracts tremendous interest for exploring novel topological quantum states and their phase transitions. Here we show by first-principles calculations and the Floquet theorem that a carbon allotrope body-centered tetragonal ${\text{C}}_{16}$ $\left(\mathrm{bct}\text{−}{\mathrm{C}}_{16}\right)$, a typical nodal-line semimetal, exhibits exotic photoinduced Floquet mixed-Weyl semimetallic features. Under the irradiation of a linearly polarized light, $\mathrm{bct}\text{−}{\mathrm{C}}_{16}$ undergoes a topological phase transition from a nodal-line semimetal to a Weyl semimetal with two pairs of tunable Weyl points. With increasing the light intensity, left-handed Weyl points evolve from type I into type II while right-handed ones are always preserved to be type I, giving rise to light-induced unconventional Weyl pairs composed of distinct types of Weyl points. Importantly, a special Weyl pair formed by type-I and type-III Weyl points is present at the critical transition point. The photon-dressed Fermi arcs connecting the projections of two different types of Weyl points are clearly visible, further revealing their unique topological features. Our work not only realizes promising unconventional Weyl pairs but also paves a reliable avenue for investigating light-induced topological phase transitions.

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• Photoinduced effect
• Topological materials
• Carbon-based materials
• Weyl semimetal
• Bloch-Floquet theorem
• Density functional theory
• Tight-binding model
• Wannier function methods