Polaritons in van der Waals materials produce an enhanced light-matter interaction that enables a vast range of applications including single-photon sources, nanolasers, and nanosensors. However, achieving customized polariton excitation across a broad spectral range within a single intrinsic platform remains challenging. Here we identify a family of two-dimensional honeycomb boron allotropes that intrinsically support spectrally customized plasmon polaritons over a wide frequency range. First-principles calculations reveal Dirac dispersions at the K point in all allotropes, with one phase hosting a Dirac cone pinned to the Fermi level. Variations in band curvature near the Fermi energy modify the carrier effective mass and interband optical transitions, thereby shifting the plasma frequency and reshaping the dielectric response. This electronic tunability directly controls the polariton dispersion and enables distinct spectral regimes within the same material system. The resulting modes exhibit low dissipative losses and long propagation lengths that surpass those of conventional noble metals such as Ag and Au. These results establish two-dimensional boron as an intrinsic platform for broadband, low-loss, and spectrally programmable polaritons.

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• Plasmonics
• Surface plasmons
• 2-dimensional systems
• First-principles calculations