Active and passive control of low-temperature thermal conduction with pillar-based phononic crystals
Ilari Maasilta
Phononic crystals (PnCs) can be used to control phonon thermal conduction, with particularly strong effects observed at low temperatures where coherent effects through modification of the phonon dispersions have been demonstrated by our group before. Earlier studies concentrated on geometries with periodic array of holes, but recently, we have studied pillar-based PnCs.
Here, I discuss recent sub-Kelvin thermal transport experiments of several nano- to microscale pillar-based PnCs, demonstrating up to an order of magnitude reduction in thermal conductance [1]. The samples consist of superconducting aluminum pillars on a suspended SiN membrane. Finite element method simulations were used to compute the phonon dispersion relations and calculate the thermal conductance of all the PnCs, and Brillouin light spectroscopy was used to validate the dispersion calculations. I also discuss our recent demonstration of active control of thermal conductance on such PnCs using a magnetic field. By switching the superconductivity of the Al pillars on and off with the applied field, we observe a sizable change in the phonon thermal conductance, a demonstration of a phonon heat switch.
[1] T. Korkiamäki et al, Comm. Phys. (2026) https://www.nature.com/articles/s42005-026-02774-6
