Metallic θ-phase tantalum nitride has a thermal conductivity triple that of copper.

Efficient heat dissipation is fundamentally limited by intrinsic scattering mechanisms that cap the thermal conductivity of metallic materials such as copper to 400 watts per meter-kelvin. Here we report the experimental realization of single-crystalline θ-phase tantalum nitride (θ-TaN), a metastable transition metal nitride predicted to overcome this limitation. We measured a room-temperature thermal conductivity of 1100 watts per meter-kelvin, nearly three times that of copper. Synchrotron-based inelastic x-ray scattering revealed a distinctive phonon band structure with a large acoustic-optical gap and phonon bunching, which suppress phonon-phonon scattering. Ultrafast optical spectroscopy confirmed exceptionally weak electron-phonon coupling and validated first-principles calculations. These findings redefine the thermal transport limits of metallic materials and open new opportunities for advancing thermal management in electronics and power systems.