Thin-film magnomechanics in the low gigahertz regime

Abstract

The coherent interaction between magnons and phonons in the low-GHz regime represents an unexplored frontier in hybrid magnonics, critical for quantum information processing and microwave-to-acoustic transduction. While previous studies have focused on higher frequencies (>5 GHz), we demonstrate magnon-phonon coupling near 2 GHz using spoof surface plasmon polariton (SSPP) waveguides integrated with yttrium iron garnet (YIG) thin films of varying thicknesses. SSPP waveguides provide strong slow-wave enhancement, enabling efficient magnon readout in this challenging regime. Systematic measurements reveal the dependence of coupling strength on YIG thickness and phonon wavelength matching, achieving cooperativity C = 1 for a 3 $\mu$m film at 2 GHz. Angle-dependent studies uncover coupling to both transverse and longitudinal phonon modes. Further investigation shows that thicker films exhibit rich multimode dynamics between high-order magnons and HBAR phonons. These results establish a robust low-GHz magnomechanical platform, opening pathways for multimode quantum transduction and hardware-efficient quantum technologies.