Demagnetization-Driven Nanoscale Chirality-Selective Phonon Transport.

Chiral-lattice degrees of freedom can offer novel chirality-selective functionalities for thermotronic applications. Chiral phonons, which carry both heat and angular momentum, can arise from broken chiral degeneracy in phonon bands or from angular momentum transfer from photons or spins. Here, we demonstrate a nanoscale chirality-selective phonon transport based on a simple heterostructure of ferromagnetic [Co/Pt] multilayers and insulating chiral α-SiO2. Using magneto-optic thermometry, we show that the effective thermal conductivity of α-SiO2 depends systematically on both the magnetization direction of [Co/Pt] and the structural handedness of α-SiO2. This behavior is supported by first-principles-based molecular dynamics simulations, which reveal chirality-dependent phonon transport across the ferromagnet/chiral-material interface. The magnetization-dependent thermal on/off ratio reaches 1.07 at room temperature and increases to approximately 1.2 at 50 K, reflecting reduced Umklapp phonon-phonon scattering. These results establish a ferromagnet/chiral-material platform for controlling nanoscale heat flow through chiral phonons.