14:00 〜 14:15
▲ [6p-C22-2] Thermal Conductance of Hole- and Pillar-Based Phononic Crystals
キーワード：phononic crystal, low temperatures, nanoscale heat transport
Phononic crystals (PnC) can effectively control heat transport at low temperatures via phonon dispersion engineered through the PnC design. PnCs, used for most of the applications, are typically two-dimensional and consist of periodic arrays of either holes in a membrane (hole-based) or pillars on top of the membrane (pillar-based). In both types of PnCs phonon dispersion can be changed due to phonon interference, which leads to the reduction of the group velocity and modifications of the density of states (DOS), thus changing thermal conductance of the structure. In this work we seek complete understanding of the processes behind the modifications of thermal transport in PnCs and systematically investigate how thermal conductance of hole- and pillar-based PnCs of realistic size depends on the various dimensions, material, lattice type and temperature.
We show that in both types of PnCs thermal conductance is suppressed in the structures of sufficiently long period (at a given temperature), yet at very low temperatures (< 0.5 K) structures with short period (< 60 nm) can on the contrary enhance thermal conductance as compared to an unpatterned membrane. In pillar-based PnCs, where the local resonances play an important role, we investigated the impact of the pillar material and size and found that the resonances actually do not suppress heat transfer, but on the contrary increase the conductance via DOS. Thus, the overall suppression of thermal conductance in pillar-based PnCs appears despite (not due to) the local resonances and is caused by periodicity of the structure. Next, we highlight the importance of critical membrane thickness below which the suppression of thermal conductance by PnCs starts growing as the thickness is decreased. Finally, we propose hybrid hole-pillar PnCs which combines both types of PnCs and demonstrates the strongest reduction of thermal conductance.
We show that in both types of PnCs thermal conductance is suppressed in the structures of sufficiently long period (at a given temperature), yet at very low temperatures (< 0.5 K) structures with short period (< 60 nm) can on the contrary enhance thermal conductance as compared to an unpatterned membrane. In pillar-based PnCs, where the local resonances play an important role, we investigated the impact of the pillar material and size and found that the resonances actually do not suppress heat transfer, but on the contrary increase the conductance via DOS. Thus, the overall suppression of thermal conductance in pillar-based PnCs appears despite (not due to) the local resonances and is caused by periodicity of the structure. Next, we highlight the importance of critical membrane thickness below which the suppression of thermal conductance by PnCs starts growing as the thickness is decreased. Finally, we propose hybrid hole-pillar PnCs which combines both types of PnCs and demonstrates the strongest reduction of thermal conductance.