Mapping phonon hydrodynamic strength in micrometer-scale graphite structures

With the peculiar collective transport behaviors and potential applications in thermal management, phonon hydrodynamics at elevated temperatures draws increasing attention in host materials, such as graphite. We map the strength of steady-state phonon hydrodynamic flow in ¹²C purified graphite micro-structures with finite length and width in a broad range of sizes and temperatures. Our theoretical modeling demonstrates that hydrodynamic phonon conduction is largely strengthened and shifts to lower temperature ranges with increasing width from a few micro-meters to 10 μm. The present work provides an insight into phonon hydrodynamics in finite-sized graphitic materials and guides its experimental observation.