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.