Polarization flip induced phonon branch decoupling and significant suppression of thermal transport behavior in α−In2Se3

The polarization transition inside ferroelectric materials can significantly affect their electronic properties, leading to wide applications in the field of nanoelectronics. However, the effect of polarization direction on thermal transport is still not well understood. In this paper, we report the effective regulation of thermal transport behavior in ferroelectric $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ by adjusting its polarization phase. In the intrinsic ferroelectric phase $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ (${\mathrm{T}}_{1}$), because of the aligned polarization direction and structural symmetry, numerous degenerate phonon branches appear in the phonon spectrum. In this case, scattering channels between coupled phonons are restricted by energy conservation requirements during the phonon scattering process. However, most of these degenerate phonon branches become significantly decoupled when the ferroelectric ${\mathrm{T}}_{1}$ phase transitions to a new stable ferrielectric ${\mathrm{T}}_{2}$ phase. As a result, a significant number of scattering channels open up, leading to a substantial increase in scattering phase space in the ${\mathrm{T}}_{2}$ structure. This enlarged scattering phase space can lead to stronger phonon anharmonic scattering and significantly suppress thermal transport. For instance, the room temperature thermal conductivity of the ${\mathrm{T}}_{2}$ phase along the interlayer direction decreases by 64% compared to the ${\mathrm{T}}_{1}$ phase. Meanwhile, phonon coherence exists in both the ${\mathrm{T}}_{1}$ and ${\mathrm{T}}_{2}$ structures, where wave-like thermal transport plays a more significant role in the ${\mathrm{T}}_{2}$ case, particularly in the interlayer direction. The insights provided by this study offers an approach for the efficient regulation of thermal transport behavior in advanced functional materials.