Lone-pair electrons induced anomalous enhancement of thermal transport in strained planar two-dimensional materials

Manipulating heat conduction is an appealing thermophysical problem with enormous practical implications, which requires insight into the lattice dynamics. Strain engineering is one of the most promising and effective routes towards continuously tuning the thermal transport properties due to the flexibility and robustness. However, previous studies mainly focused on quantifying how the thermal conductivity is affected by strain, while the fundamental understanding on the electronic origin has yet to be explored. In this talk, I would like to show that the thermal conductivity (κ) of planar monolayer group III-nitrides is unexpectedly enlarged by one order of magnitude with bilateral tensile strain applied, which is in sharp contrast to the strain induced κ reduction in graphene despite their similar planar honeycomb structure. The anomalous positive response of κ to tensile strain is attributed to the attenuated interaction between the lone-pair s electrons around N atoms and the bonding electrons of neighboring (B/Al/Ga) atoms, which reduces phonon anharmonicity. The microscopic picture for the lone-pair electrons driving phonon anharmonicity would have great impact on future research in materials design with targeted thermal transport properties.