Monday, February 17 2020
14:00 - 15:30

Alladi Ramakrishnan Hall

Microscopic view of heat conduction in solids

Navaneetha K. Ravichandran

IISc, Bangalore

Microscopic quantum mechanical interactions among heat carriers called phonons govern the macroscopic thermal properties of semiconducting and electrically insulating crystalline solids, which find applications in thermal management of electronics, thermal barrier coatings and thermoelectric modules. In this talk, I will first describe my recent work on how our newly developed first-principles computational framework to predict these microscopic interactions among phonons unveils a new paradigm for heat conduction in several of these materials. As an example, I will describe a curious case of heat conduction in the ultrahigh thermal conductivity material - boron arsenide (BAs), where the lowest order interactions involving three phonons are unusually weak and higher-order scattering among four phonons affects the thermal conductivity significantly, in stark contrast with other ultrahigh thermal conductivity materials like diamond and boron nitride [1, 2]. I will show that this competition between three and four phonon scattering can be exquisitely tuned with the application of hydrostatic pressure, resulting in an unusual non-monotonic pressure dependence of the thermal conductivity in BAs unlike in most other materials [3]. Finally, I will describe my prior experimental effort to probe the scattering of THz-frequency thermal phonons at atomically rough surfaces of a nanoscale silicon film using a non-contact optical pump-probe experiment called the transient grating. Through these measurements, I will show that the surface scattering behavior of the heat-carrying thermal phonons is extremely sensitive to the changes in surface roughness of just a few atomic planes even at room temperature [4].

References [*: Equal Contribution]:

[1] Fei Tian, Bai Song, Xi Chen, Navaneetha K. Ravichandran et al., Science 361 (6402), 582-585, 2018

[2] Ke Chen*, Bai Song*, Navaneetha K. Ravichandran* et al., Science 367 (6477), 555-559, 2020

[3] Navaneetha K. Ravichandran & David Broido, Nature Communications 10 (827), 2019

[4] Navaneetha K. Ravichandran, Hang Zhang & Austin Minnich, Physical Review X 8 (4), 041004, 2018

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