θ-TaN: Redefining the Thermal Conductivity Limit of Metallic Materials

• θ-TaN achieves a room-temperature thermal conductivity of ~1100 W·m⁻¹·K⁻¹, nearly three times that of copper, shattering the long-standing limit for metals. • The ultrahigh thermal conductivity is phonon-dominated, enabled by a large acoustic-optical phonon gap and acoustic phonon bunching that suppress phonon-phonon scattering. • High-quality single crystals of metastable θ-TaN were synthesized via a flux-assisted metathesis reaction, overcoming challenges of conventional high-pressure routes. • This discovery validates theoretical predictions and opens new avenues for thermal management in high-power electronics and other applications.