Numerical Modeling of the Ultrafast Plasmonic Response of Titanium Nitride Nanostructures

Titanium nitride (TiN) is a promising plasmonic material that has come into the spotlight as a valid alternative to noble metals. As for other plasmonic materials, great attention has been given to the development of TiN nanostructures so as to efficiently tune the plasmon resonance, also combining them in lattices and with other metals or semiconductors. In addition, TiN boasts carrier cooling dynamics more than one order of magnitude faster than that of gold, which gives it a clear advantage in many applications. However, the knowledge of the ultrafast optical response of TiN nanostructures is narrowed down to experimental evidence, without a complete modeling. In this work, we numerically model the nonequilibrium hot-carrier-mediated mechanisms and ultrafast nonlinear changes in the optical response of TiN nanostructures photoinduced by femtosecond laser pulses. Specifically, we focus on nanodisks and nanospheres and compare our simulations with experimental pump-probe measurements. Our approach enables us to disentangle the interband and intraband contributions to the permittivity modulation, pointing out the critical role of the interplay between the TiN interband transitions and the nanostructure optical resonances in the early stages of the photoinduced ultrafast dynamics.