"Hot" Carriers in Nanostructures – When they matter, and when they do not...

In the last couple of decades, non-thermal (“hot”) carriers in nanostructures have been simultaneously an inspirational concept to which a series of effects were ascribed, but also a source of confusion and hot debates. My talk will be aimed at describing the advances we obtained in the understanding of the role played by “hot” carriers in metals as well as transparent oxides via rigorous modelling of their generation process and dynamics, and extensive comparison to previous and new collaborative experimental work.

I will start by presenting a self-consistent theory of the steady-state electron distribution in metals under continuous-wave illumination which treats, for the first time, both thermal and non-thermal effects on the same footing. I will show that the number of non-thermal electrons is very small (i.e., the deviation from thermal equilibrium is weak), so that the power that ends up generating these non-thermal electrons is many orders of magnitude smaller than the amount of power that leads to regular heating [1]. I will then review recent experimental quantitative confirmations of our theory obtained in current measurements through a plasmonic molecular and tunnel junctions [2].

Then, I shall discuss reports of observation of nonthermal electrons in two classes of experiments. First, I will review briefly our (unfortunately discouraging...) re-interpretation of previous claims of the possibility to enhance chemical reactions with non-thermal electrons from metals as nothing but pure thermal effects [3]. Then, I will show that non-thermal electrons do manifest themselves in metal photoluminescence experiments, explain why they sometime “look” like thermal carriers and resolve the many decade-long disagreements in the literature [4].

The latter discussion, which will involve also the ultrafast electron and light emission dynamics, will lead me to describe briefly new results on the nonlinear optical response of transparent conducting oxides [5] as well as emerging work where we look at single cycle and attosecond pulse dynamics in those materials.

References
[1] Dubi & Sivan, Light: Science & Applications 8, 89 (2019).
[2] Dubi, Un & Sivan, Nano Letters 22, 2127 (2022); Lin et al., ACS Photonics 10, 3637 (2023).
[3] Sivan & Dubi, Applied Physics Letters: Perspectives 117, 130501 (2020).
[4] Sivan & Dubi, ACS Nano 15, 8724 (2021).
[5] Sarkar, Un & Sivan, Phys. Rev. Applied 19, 014005 (2023).