Microscopic view of heat conduction in solids by Dr. Navaneetha Ravichandran

Location and Date: 
Friday, 12 April, 2019, 12:00-01:00 pm, Seminar Hall, Second Floor, DESE-CESE Building
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 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 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 several other semiconductors such as silicon and diamond [1]. 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 [2]. I will also briefly describe my prior experimental effort to probe the scattering of phonons at atomically rough surfaces of a nanoscale silicon film, where they showed extreme sensitivity to the changes in surface roughness of just a few atomic planes [3]. Finally, I will motivate my current work and future research directions of consolidating these experimental and computational advances to probe the interactions of phonons with other forms of energy carriers such as electrons in semiconductors and metals, at high temperatures and extreme environmental conditions.
[1] Fei Tian, Bai Song, Xi Chen, Navaneetha K. Ravichandran et al., Science 361 (6402), 582-585, 2018
[2] Navaneetha K. Ravichandran & David Broido, Nature Communications 10 (827), 2019
[3] Navaneetha K. Ravichandran, Hang Zhang & Austin Minnich, Physical Review X 8 (4), 041004, 2018

I obtained my Dual Degree (B. Tech and M. Tech) in Mechanical Engineering from the Indian Institute of Technology, Madras. I obtained my Masters in Space Engineering and PhD in Mechanical Engineering from Caltech, working with Prof. Austin Minnich. For my PhD, I worked on experimentally investigating phonon boundary scattering in thin silicon membranes using the transient grating experiment. I am currently a postdoctoral fellow at Boston College, where I am working with Prof. David Broido on developing a predictive first-principles computational framework to capture the thermal and electronic properties of materials at high temperatures and extreme environmental conditions.