Modulating phonon transport in bilayer black phosphorus: Unraveling the interplay of strain and interlayer quasicovalent bonds

Efficient thermal management in nanoscale electronic devices presents a pressing challenge. The two-dimensional (2D) materials, notably bilayer black phosphorus, exhibit unique thermal properties that hold promise for addressing this challenge. In this study, we explore the impact of the strain on phonon hydrodynamics in bilayer black phosphorus, providing insight into its intricate thermal behavior. By employing first-principles calculations and the Boltzmann transport equation, we uncover that the thermal conductivity generally decreases with increasing strain. However, a nonmonotonic behavior emerges at small strains, challenging conventional expectations. This behavior is attributed to the intricate interplay among the softening of optical phonons induced by strain, the subsequent enhancement of phonon scattering, and the maintenance/strengthening of the quadratic Z-axis acoustic (ZA) mode through reinforced quasicovalent bonds, ultimately contributing to improved phonon hydrodynamics. Our findings underscore the pivotal role of interlayer thickness in governing these effects. Our research pioneers the modulation of phonon hydrodynamics, offering transformative insight into the 2D materials' thermal behavior.