The phonon quantum of thermal conductance: Are simulations and measurements estimating the same quantity?

International audienceThe thermal conductance quantum is a fundamental quantity in quantum transport theory. However, two decades after its first reported measurements and calculations for phonons in suspended nanostructures, reconciling experiments and theory remains elusive. Our massively parallel calculations of phonon transport in micrometer-sized three-dimensional structures suggest that part of the disagreement between theory and experiment stems from the inadequacy of macroscopic concepts to analyze the data. The computed local temperature distribution in the wave ballistic nonequilibrium regime shows that the spatial placement and dimensions of thermometers, heaters, and supporting microbeams in the suspended structures can noticeably affect the thermal conductance’s measured values. In addition, diffusive transport assumptions made in the data analysis may result in measured values that considerably differ from the actual thermal conductance of the structure. These results urge for experimental validation of the suitability of diffusive transport assumptions in measuring devices operating at sub-kelvin temperatures

Suspended crystalline silicon thermometry devices: towards quantum nanophononics

posterInternational audienceThis work addresses the current experimental gap in thermal transport regimes and phonon transport at low temperatures and small scales. These conditions cause the wavelength λ and mean free pass Λ of phonons to become equal or greater than the sample’s dimensions, giving rise to several interesting quantum phenomena, hence the name quantum nanophononics. Multiple phenomena are expected to be studied : Phonon interferometric effects [1], thermal rectification, quantization of thermal transport, etc..

Suspended crystalline silicon thermometry devices: towards quantum nanophononics

posterInternational audienceThis work addresses the current experimental gap in thermal transport regimes and phonon transport at low temperatures and small scales. These conditions cause the wavelength λ and mean free pass Λ of phonons to become equal or greater than the sample’s dimensions, giving rise to several interesting quantum phenomena, hence the name quantum nanophononics. Multiple phenomena are expected to be studied : Phonon interferometric effects [1], thermal rectification, quantization of thermal transport, etc..

Suspended crystalline silicon thermometry devices: towards quantum nanophononics

posterInternational audienceThis work addresses the current experimental gap in thermal transport regimes and phonon transport at low temperatures and small scales. These conditions cause the wavelength λ and mean free pass Λ of phonons to become equal or greater than the sample’s dimensions, giving rise to several interesting quantum phenomena, hence the name quantum nanophononics. Multiple phenomena are expected to be studied : Phonon interferometric effects [1], thermal rectification, quantization of thermal transport, etc..

Experimental evaluation of thermal rectification in a ballistic nanobeam with asymmetric mass gradient

International audiencePractical applications of heat transport control with artificial metamaterials will heavily depend on the realization of thermal diodes/rectifiers, in which thermal conductivity depends on the heat flux direction. Whereas various macroscale implementations have been made experimentally, nanoscales realizations remain challenging and efficient rectification still requires a better fundamental understanding of heat carriers' transport and nonlinear mechanisms. Here, we propose an experimental realization of a thermal rectifier based on two leads with asymmetric mass gradients separated by a ballistic spacer, as proposed in a recent numerical investigation, and measure its thermal properties electrically with the microbridge technique. We use a Si 3 N 4 nanobeam on which an asymmetric mass gradient has been engineered and demonstrate that in its current form, this structure does not allow for thermal rectification. We explain this by a combination of too weak asymmetry and non-linearities. Our experimental observations provide important information towards fabricating rigorous thermal rectifiers in the ballistic phonon transport regime, which are expected to open new possibilities for applications in thermal management and quantum thermal devices

Crystalline silicon based suspended thermometry platforms: study of quantum phononic effects

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Crystalline silicon based suspended thermometry platforms: study of quantum phononic effects

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A sensor for manipulation of heat carried by phonons at the nanoscale and very low temperature

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Phonon transport in asymmetric nanostructures in the ballistic regime

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Heat manipulation at the nanoscale in the ballistic regime

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