In a recent article in Nature Materials, researchers explored a novel approach to boosting thermal transport across solid interfaces by activating hyperbolic phonon-polariton (HPhP) modes in hexagonal boron nitride (hBN). The study shows that these hybrid light–vibration modes can transfer energy at rates far exceeding conventional phonon–phonon conduction.
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Background: The Need for Faster Thermal Transport
Efficient heat dissipation across solid–solid interfaces is a critical challenge in the design of high-performance electronics and optoelectronics. Traditional heat conduction relies primarily on acoustic phonons, but these mechanisms often fall short, especially at heterogeneous dielectric interfaces, where thermal boundary conductance (TBC) tends to be limited.
Earlier work has shown that HPhPs in hBN can propagate over long distances, with potential applications in hyperlensing, infrared imaging, and chemical sensing. These modes also appear promising for thermal transport, particularly where phonon-based conduction underperforms.
There is growing evidence that phonon-polariton interactions can occur at interfaces involving 2D van der Waals materials, but extending this understanding to three-dimensional contacts remained largely unexplored.
The researchers hypothesize that evanescent fields generated by hot carriers can directly couple with HPhPs, bypassing the bottlenecks of conventional phonon transmission and offering a more rapid channel for thermal energy flow.
The Study: Probing Ultrafast Heat Transfer at Interfaces
To investigate this mechanism, the team used a pump–probe thermoreflectance technique with sub-picosecond time resolution. A thin gold (Au) pad served as the heat source, excited by a 520 nm laser pulse.
A mid-infrared probe beam with a diameter of 200 μm was focused onto the same pad to track changes in reflectance over time, offering insights into how thermal energy moved from the Au into the adjacent hBN layer.
To interpret the data, the researchers applied a transfer matrix method (TMM) to model the thermoreflectance response. They focused on the spectral range near hBN’s Reststrahlen band, where HPhPs are known to be active. This allowed them to distinguish between high-momentum excitations that can couple to HPhPs and those that cannot.
Results and Discussion
The results confirmed that thermal energy from the heated Au pad could efficiently couple into HPhP modes in hBN, bypassing slower phonon conduction pathways. The hot electrons in Au radiated energy directly into polaritonic modes at the interface, enabling a thermal transport rate nearly an order of magnitude faster than traditional phonon mechanisms.
Measured thermal boundary conductance reached approximately 100 MW m⁻² K⁻¹, far surpassing typical values for phonon-only transmission across the same materials. These findings support the idea that non-radiative coupling between electrons and polaritons at a solid–solid interface can open new channels for ultrafast thermal transport.
The study also emphasizes the technological implications of these findings. In high-frequency or high-power devices, where heat builds up rapidly, traditional cooling methods often fail to respond in time. Using polaritonic modes to channel thermal energy away from hotspots could provide a powerful alternative, enabling more effective thermal management in compact or demanding systems.
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Conclusion
This work marks a significant advancement in understanding interfacial heat transfer. By coupling thermal energy into hyperbolic phonon-polaritons, the researchers demonstrated that hBN can act as a high-performance medium for ultrafast thermal dissipation, far beyond what is achievable with conventional phonon-based models.
The findings lay the foundation for deeper investigations into polariton–phonon interactions, and open up opportunities to design materials and interfaces that can be tuned for optimal thermal performance. Applications range from transducer cooling to advanced photonic integration, where precise heat management is critical.
As the field moves beyond traditional models of heat conduction, this study suggests that polaritonic coupling could redefine how we approach thermal regulation in devices.
Journal Reference
Hutchins W., et al. (2025). Ultrafast evanescent heat transfer across solid interfaces via hyperbolic phonon–polariton modes in hexagonal boron nitride. Nature Materials. DOI: 10.1038/s41563-025-02154-5, https://www.nature.com/articles/s41563-025-02154-5