Unusual Temperature-Dependent Thermal Conductivity in Monolayer NCCN: Role of Phonon Hydrodynamics

Seeking high-thermal-conductivity materials is a route to enhancing the efficiency of heat dissipation in Ga-based high-power-density devices. In this work, we use first-principles calculations with the Boltzmann transport equation to predict the thermal conductivity of nitrogen-substituted diamane (NCCN). It is found that the thermal conductivity (κ) of NCCN is as high as 1800 W/mK at room temperature, which is 13.7% smaller compared to that before considering four-phonon scattering. Moreover, there is an anomalous temperature dependence of κ, inconsistent with the typical κ ∼ 1/T trend. This unusual phonon transport behavior stems from the significant hydrodynamic phonon transport in NCCN, where momentum-conserving N-scattering is a dominant scattering mechanism. More importantly, NCCN demonstrates promising potential for hydrodynamic phonon transport above room temperature and over a broader temperature window compared to that of graphene. With the application of tensile strain, the anomalous temperature dependence of κ is subject to change, as longitudinal acoustic and transverse acoustic phonon softening offsets the effects of flexural acoustic-mode linearization, resulting in a decrease in κ with increased strain. Our conclusion could assist the future exploration of hydrodynamic thermal transport behaviors in 2D materials.