High thermal conductivity in metallic θ-TaN single crystals

Metallic materials are critical in integrated circuits as they not only deliver electricity but also dissipate heat. However, their performance is constrained as the thermal conductivity of metals is capped with a value of ∼400 W m^{- 1} K^{- 1}. Here, we shatter this long-standing ceiling by high-pressure synthesis of the metallic hexagonal tantalum mononitride (θ-TaN) single crystal with ultrahigh thermal conductivity. The synthesized θ-TaN single crystal exhibits a room-temperature thermal conductivity of 502 W m^{- 1} K^{- 1}, exceeding the conventional upper limit for metallic thermal conductors, despite the presence of a substantial concentration of nitrogen vacancies. Our findings identify a clear pathway for further enhancing thermal conductivity through minimizing vacancy concentration in θ-TaN. This work establishes θ-TaN as a highly promising candidate for advanced thermal management applications and introduces a new approach for designing metallic conductors to surpass conventional limits.