Heat conduction measurements in ballistic 1D phonon waveguides indicate breakdown of the thermal conductance quantization

Abstract

Emerging quantum technologies require mastering thermal management, especially at the nanoscale. It is now accepted that thermal metamaterial-based phonon manipulation is possible, especially at sub-kelvin temperatures. In these extreme limits of low temperatures and dimensions, heat conduction enters a quantum regime where phonon exchange obeys the Landauer formalism. Phonon transport is then governed by the transmission coefficients between the ballistic conductor and the thermal reservoirs. Here we report on ultra-sensitive thermal experiments made on ballistic 1D phonon conductors using a micro-platform suspended sensor. Our thermal conductance measurements attain a power sensitivity of 15 attoWatts around 100 mK. Ballistic thermal transport is dominated by non-ideal transmission coefficients and not by the quantized thermal conductance of the nanowire itself. This limitation of heat transport in the quantum regime may have a significant impact on modern thermal management and thermal circuit design.

Crossover between Electron-Phonon and Boundary-Resistance Limits to Thermal Relaxation in Copper Films

“…Especially for mesoscopic devices at low temperature, where the dominant thermal wavelength λ is comparable to the device dimension, phonons in the films could be twodimensional (2D), and it has been shown both experimentally and theoretically that the reduced phonon dimension does affect the energy relaxation of electrons in thin films [5][6][7][8]. Heat transport by phonons, electrons, and photons has been studied experimentally in mesoscopic devices [9][10][11][12][13][14]. From the application point of view, a good understanding of energy relaxation in metal films is important, e.g., for calorimetry and bolometry [15].…”

Niobium Nitride Thin Films for Very Low Temperature Resistive Thermometry

“…Regarding the coupling between the phonon baths in the NbN and in the silicon substrate, a rough estimate of the Kapitza thermal conductance indicates an expected thermal conductance of the solid-solid contact between NbN and Si or SiN of K Kapitza = 1.4 × 10 −10 W.K −1 [36]. This analysis shows that micrometer size thermometers can be prepared and used for very low temperature physics under the careful choice of the measuring currents [28,25].…”

“…Fig. 1 shows the versatility of the NbN deposition; two examples of thermometers are given, one on the millimetric size with deposition done on silicon substrate (caped with 100 nm of SiN for electrical isolation), the other on the micrometer size with a NbN thermometer included on a SiN membrane calorimetric suspended sensor [25].…”

2D Phononic Crystals: Progress and Prospects in Hypersound and Thermal Transport Engineering

“…This demonstration opened the path to an enhanced control of heat transport as will be discussed in Section . Decreasing further the phonon population in the mK range attempts were made to observe the quantization of heat for which both low temperatures and small dimensions are required. Despite a clear ballistic signature in these experiments, the debate is still ongoing over the observation of the quantum of thermal conductance.…”