Demagnetization-Driven Nanoscale Chirality-Selective Thermal Switch

Chiral-lattice degrees of freedom can offer novel chirality-selective functionalities for thermotronic applications. Chiral phonons, carrying both heat and angular momentum, can emerge through a breaking of chiral degeneracy in the phonon bands, either via an intrinsic chiral crystal structure or by angular momentum transfer from photons or spins. This chiral controllability of the lattice dynamics enables a design of chiral thermo-devices by integrating ferromagnets with chiral materials. Here, we present a nanoscale chirality-selective thermal switch realized using a simple heterostructure composed of ferromagnetic [Co/Pt] multilayers and insulating chiral $α$-SiO2, where an external magnetic field can control thermal transport properties. Our experimental results based on the magneto-optic thermometry reveal that the thermal conductivity of $α$-SiO2 exhibits a clear dependence on both the magnetization direction of [Co/Pt] multilayers and the structural chirality of $α$-SiO2, which is supported well by the first-principles-based molecular dynamic simulations. The magnetization-dependent thermal on/off ratio amounts to 1.07 at room temperature and increases to about 1.2 as temperature decreases to 50 K, due to a reduction of Umklapp phonon-phonon scattering rate in $α$-SiO2. These findings provide the first experimental demonstration of the nanoscale chirality-selective thermal switch based on the ferromagnetic/chiral material heterostructure, highlighting its potential as a key technology for addressing heat dissipation challenges in nanoscale electronic devices.