Materials Research Lecture

How does an excited electron lose its energy? This problem is central in fields ranging from condensed matter physics to electrical engineering and energy. The talk will discuss calculations of the dynamics of out-of-equilibrium charge carriers – also known as hot carriers (HCs) – in semiconductors and metals [1–3]. We will focus on first-principles calculations of electron-phonon, electron-electron, and electron-defect scattering that can predict the relaxation times and mean free paths of HCs in materials. This framework is applied to: 1) HC thermalization in the first picosecond after sunlight absorption in silicon. 2) HCs in GaAs, for which our results contribute to resolve experimental controversies and challenge the tenet that optical lattice vibrations are mainly responsible for energy loss. 3) HCs generated by surface plasmons in noble metals, a process of relevance in optoelectronics and photocatalysis, for which we predict optimal conditions for HC generation and extraction.

We will show how the concepts introduced in the talk can be extended to model electron transport and exciton dynamics [4] from first principles. The talk will conclude with an outlook of the challenges to compute electron dynamics from first principles.

[1] M. Bernardi et al., Phys. Rev.Lett. 112, 257402 (2014).
[2] M. Bernardi et al., PNAS. 112, 5291 (2015).
[3] M. Bernardi et al., Nature Commun. 6:7044 (2015).

[4] M. Palummo, M. Bernardi, and J. C. Grossman, Nano Lett. 15, 2794 (2015).

More about the speaker:

Marco Bernardi is Assistant Professor in the Department of Applied Physics and Materials Science at Caltech since Sept. 2015. He specializes in theoretical / computational materials science and condensed matter physics. He obtained his Ph.D. in Materials Science from MIT, where he worked with Prof. Jeff Grossman on novel materials and physical processes in solar energy conversion. He was a postdoc in the Physics Department at UC Berkeley, where he worked with Prof. Steve Louie and Prof. Jeff Neaton on excited electrons in materials. His group at Caltech focuses on computing the dynamics of excited states and ultrafast processes in materials.

Marco has received a number of awards, including the 2015 Psi-K Volker Heine Young Investigator Award for electronic structure calculations, the Intel Ph.D. Fellowship from Intel, and the Endeavour Research Fellowship from the Australian Government, among others. His research has been featured in a number of magazines, including Wired, Nature, Scientific American, and Technology Review.