Abstract
As a foundational concept in many-body physics, electron–phonon interaction is essential to understanding and manipulating charge and energy flow in various electronic, photonic, and energy conversion devices. While much progress has been made in uncovering how phonons affect electron dynamics, it remains a challenge to directly observe the impact of electrons on phonon transport, especially at environmental temperatures. Here, we probe the effect of charge carriers on phonon heat transport at room temperature, using a modified transient thermal grating technique. By optically exciting electron-hole pairs in a crystalline silicon membrane, we single out the effect of the phonon–carrier interaction. The enhanced phonon scattering by photoexcited free carriers results in a substantial reduction in thermal conductivity on a nanosecond timescale. Our study provides direct experimental evidence of the elusive role of electron–phonon interaction in phonon heat transport, which is important for understanding heat conduction in doped semiconductors. We also highlight the possibility of using light to dynamically control thermal transport via electron–phonon coupling.
Highlights
As a foundational concept in many-body physics, electron–phonon interaction is essential to understanding and manipulating charge and energy flow in various electronic, photonic, and energy conversion devices
We experimentally quantify the effects of optically excited free carriers on collective phonon dynamics in silicon, revealing the direct impact of electron–phonon interactions on heat transport
We describe a time-resolved optical measurement to quantify the effect of electron–phonon interactions on heat transport in a crystalline silicon membrane, and demonstrate a significant reduction in the thermal conductivity at room temperature with good agreement between experiment and first principles calculation
Summary
As a foundational concept in many-body physics, electron–phonon interaction is essential to understanding and manipulating charge and energy flow in various electronic, photonic, and energy conversion devices. Carrier effects on optical phonons with terahertz frequencies can be probed by transient Raman scattering[15], to investigate the population and relaxation of select phonon modes out of equilibrium[16] Despite these studies demonstrating the importance of electron–phonon interactions in governing specific phonon states, their impacts on heat conduction have been largely overlooked. Theoretical studies by Sommerfeld and Bethe on metals[17], and by Ziman on semiconductors[18], mostly concluded that the electron–phonon interactions only have significant impacts on phonon heat conduction when the intrinsic phonon–phonon interactions become weaker at low temperatures and no longer dominate the phonon scatterings[19,20] This has been corroborated by experimental studies on metals at cryogenic temperatures, in which a strong magnetic field was used to ‘freeze out’ the electrons[21] and measure the change in the thermal conductivity[22]. Direct experimental verification of the impact of electron–phonon interactions on heat transport has been lacking
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