Controlling thermal conductance using three-dimensional phononic crystals

TL;DR

This paper demonstrates that three-dimensional phononic crystals can effectively control thermal conductance at the nanoscale, expanding possibilities for device engineering beyond suspended structures, with experimental evidence showing conductance enhancement.

Contribution

It introduces the use of three-dimensional phononic crystals for thermal conductance control, a novel approach compared to previous two-dimensional structures.

Findings

Thermal conductance can be enhanced using 3D phononic crystals.

Experimental results at sub-Kelvin temperatures confirm the effect.

Simple coherent phonon band structure theories do not fully explain the results.

Abstract

Controlling thermal transport at the nanoscale is vital for many applications. Previously, it has been shown that this control can be achieved with periodically nanostructured two-dimensional phononic crystals, for the case of suspended devices. Here we show that thermal conductance can also be controlled with three-dimensional phononic crystals, allowing the engineering of the thermal contact of more varied devices without the need of suspension in the future. We show experimental results measured at sub-Kelvin temperatures for two different period three-dimensional crystals, as well as for a bulk control structure. The results show that the conductance can be enhanced with the phononic crystal structures in our geometry. This result cannot be fully explained by the simplest theory taking into account the coherent modification of the phonon band structure, calculated with finite element method simulations.