Moiré Pattern Controlled Phonon Polarizer Based on Twisted Graphene

ZH Qin and LY Dai and M Li and SX Li and H Wu and KE White and G Gani and PS Weiss and YJ Hu, ADVANCED MATERIALS, 36 (2024).

DOI: 10.1002/adma.202312176

Twisted van der Waals materials featuring Moire patterns present new design possibilities and demonstrate unconventional behaviors in electrical, optical, spintronic, and superconducting properties. However, experimental exploration of thermal transport across Moire patterns has not been as extensive, despite its critical role in nanoelectronics, thermal management, and energy technologies. Here, the first experimental study is conducted on thermal transport across twisted graphene, demonstrating a phonon polarizer concept from the rotational misalignment between stacked layers. The direct thermal and acoustic measurements, structural characterizations, and atomistic modeling, reveal a modulation up to 631% in thermal conductance with various Moire angles, while maintaining a high acoustic transmission. By comparing experiments with density functional theory and molecular dynamics simulations, mode-dependent phonon transmissions are quantified based on the angle alignment of graphene band structures and attributed to the coupling among flexural phonon modes. The agreement confirms the dominant tuning mechanisms in adjusting phonon transmission from high- frequency thermal modes while having negligible effects on low-frequency acoustic modes near Brillouin zone center. This study offers crucial insights into the fundamental thermal transport in Moire structures, opening avenues for the invention of quantum thermal devices and new design methodologies based on manipulations of vibrational band structures and phonon spectra. For the first time, thermal experiment in twisted graphene is reported, measuring Moire angle-depedent thermal conductance and revealing fundamental relationship between twist angles and phonon behaviors. As revealed by experimental measurements and atomistic calculations, the dominant tuning mechanisms for tuning phonon transmission stem from high-frequency thermal modes while negligible effects on low-frequency acoustic modes near Brillouin zone center. This study offers crucial insights into mode-depedent thermal transport in Moire structures, opening avenues for the invention of quantum devices and new design methodologies based on manipulations of vibrational band structures and phonon spectra. image

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