Thermoplasmonics utilize excitation and damping of surface plasmons to convert light into localized heat, offering a promising route for high‐efficiency solar photothermal conversion. However, the limited infrared plasmonic response and inherent insufficient thermal effect in plasmonic materials impede the simultaneous realization of broadband absorption, spectral selectivity, and angular robustness. We identify ruthenium (Ru) as a promising refractory plasmonic material exhibiting dual epsilon‐near‐zero optical topological transitions and dual plasmonic resonances spanning from visible to infrared region with high imaginary permittivity to maximize light–heat conversion. We demonstrate a nanoparticle‐on‐cavity (NPoC) resonance configuration that synergically couples broadband hybridized nanoparticle‐on‐mirror mode and spectral‐selective spoof surface plasmon polariton mode, yielding near‐unity, spectrally selective broadband absorption. We fabricate the Ru NPoC absorber using a cost‐effective additive nanomanufacturing approach based on laser‐interference nanopatterned carbon nanotube growth followed by infiltration of Ru through conformal atomic layer deposition. The fabricated Ru NPoC absorber achieves a total solar absorptance of 96.6% and a narrow spectral transition bandwidth of 1.1 μm with angular robustness. By leveraging refractory plasmonics with deterministic mode coupling, this work establishes a versatile framework for engineered light–matter interaction, opening pathways toward dynamic thermal emitters, high‐temperature photothermal catalysis, and next‐generation solar energy harvesting.
Huang et al. (Wed,) studied this question.