Excitations of a material using visible light pulses generate electronic heating, which transient electronic temperatures largely exceeding the one of the underlying atomic lattice.
In the case of metals, Allen showed  that the subsequent equilibration between the "hot" electrons and "cold" lattice vibrations can be understood with a two-temperature (2T) picture, in which electrons and phonons remain in distinct thermal equilibria. In this talk, I will show the limitations of this physical picture when applied to semiconductors and low-dimensional materials -- materials with reduced dielectric screening, anisotropy, and, in some cases, higher lattice thermal conductivity. Based on first-principles calculations and the semiclassical Boltzmann transport equations for electrons and phonons, I will propose a generalized 2T model which captures the full thermal relaxation of hot electrons and holes, and discuss its consequences on measuring electron-phonon and phonon-phonon couplings from time-resolved spectroscopy experiments . Finally, I will show how such findings can be used to generate non-classical electron-induced heat which can be observed in experiments [3,4].  P. B. Allen, Phys. Rev. Lett. 59, 1460 (1987),  S. Sadasivam, et al. Phys. Rev. Lett. 119, 136602 (2017),  I.C. Tung, et al. Nat. Photonics, (2019),  P. Guo et al. Nat. Comm. 9 (1), 2019 (2018)
Bio: Pierre Darancet is an Assistant Scientist at the Center for Nanoscale Materials at Argonne National Laboratory and a fellow at the Northwestern-Argonne Institute for Science and Engineering. He obtained his PhD in 2008 at the Institut Néel in Grenoble before working as a postdoctoral fellow at Lawrence Berkeley National Lab and at Columbia University. His research focuses on the first-principles modeling of charge and energy transport in nanoscale materials and interfaces.