Researchers have created a technique to manage how heat flows within crystals. This compact device could be used to develop sophisticated thermal management systems in electronic gadgets, helping to avoid overheating.
Excessive heat in electronic parts can negatively impact the performance of various devices. For instance, the speed and memory capabilities of silicon-based computer chips are significantly influenced by their heat dissipation ability. Despite the high demand for better solutions, managing heat remains a complicated issue.
A recent study published in Nature by a research team led by the Institute of Industrial Science at the University of Tokyo has shown how to control heat transfer in graphite crystals. They have utilized principles from fluid dynamics to interact with phonons in solid-state crystals.
Phonons are known as ‘quasiparticles’ and represent the collective vibration of atoms or molecules within solid materials. Crystals are composed of orderly repeating patterns of atoms dispersed uniformly throughout their structure.
“In a crystal, atomic bonds function similarly to springs when atoms vibrate — for instance, when heated. These ‘springs’ work together to create a wave, or phonon, that propagates through the crystal,” clarifies Xin Huang, the lead author of the research.
Interestingly, phonons can traverse solid crystals in a way that closely mirrors fluid flow, a phenomenon termed ‘hydrodynamic phonon transport’. Huang and his team have taken advantage of this effect to achieve thermal rectification in graphite.
They designed structures similar to Tesla valves, which were originally invented by Nikola Tesla in the 1920s. Tesla’s ‘valvular conduit’ is able to direct fluid flow, making it speedier in one direction compared to the other. This principle can also facilitate thermal flow via phonons in a crystal, promoting more even heat distribution.
The thermal conductivity of the Tesla valve, which refers to a material’s ability to conduct heat, was evaluated across a temperature spectrum from 10 K to 300 K. Its non-symmetrical structure allows smooth hydrodynamic phonon transport in one direction while impeding the reverse flow. The efficiency of this rectification, known as ‘diodicity’, is represented by the ratio of thermal conductivity in both directions.
At lower temperatures of 10 K, the diodicity measured at 1. As the temperature rose, this parameter peaked at 1.15 (at 45 K), indicating that heat flowed more effectively in the forward direction. This phenomenon was observable up to 60 K, but at higher temperatures, phonon scattering led to equal thermal conductivity in both directions.
Currently, the utilization of this technology is confined to low temperatures and specific materials that demonstrate hydrodynamic phonon transport, which does not include silicon.
“What’s thrilling is that, in theory, there are no obstacles to achieving thermal rectification across a broader temperature range, potentially even at room temperature,” notes Masahiro Nomura, the senior author.
Beyond the foundational research in condensed matter physics, this discovery could eventually be harnessed across a variety of devices, allowing manufacturers to create advanced thermal management solutions that enhance the efficiency of electronic components like smartphones, computers, and LEDs.
