Stochastic Thermodynamics Analysis of Ultrafast AgAu Nanoshell Dynamics in the Nonlinear Response Regime

The understanding of relaxation dynamics of metallic nanoshells is important for a range of nanotechnological applications. In this work, we present a combined experimental-theoretical study of the relaxation dynamics of AgAu nanoshells. This was investigated using ultrafast pump-probe experiments resonant with the surface plasmon of the nanoshells, as well as via atomistic molecular dynamics simulations of relaxation and temperature-jump (DT-jump) processes. Both techniques were then discussed and complemented using a non-equilibrium statistical mechanical model. Data collected at low energies were consistent with our previously reported work and allowed the characterization of intrinsic electron-phonon coupling times (EPCT) and of the overall relaxation dynamics in terms of a two-temperature model. Data at intermediate and higher energies, in turn, showed a nonlinear dependence of EPCT as a function of the pump power, faster relaxation being observed at higher pump energies. In the limit of small DT-jumps, relaxation based on a two-temperature model is recovered, whereas in the limit of large DT-jumps, the relaxation becomes faster with increasing temperature change. The results reported here give insight on the ultrafast dynamics of AgAu nanoshells and might also be applied to other metallic systems, paving the way to the better understanding of relaxation dynamics of nanoparticles in general.