Carrier dynamics in ultrathin gold nanowires: Role of Auger processes

Carrier dynamics in metallic nanostructures is strongly influenced by their confining dimensions. Gold nanoparticles of size ∼ 2 nm lie at the boundary separating metallic and non-metallic behavior. Here, we examine the carrier dynamics in high aspect ratio ultrathin gold nanowires (Au-UNWs) of average diameter ∼2 nm using pump (3.1 eV) and coherent white-light continuum as a probe in the spectral range of 1.15 eV to 2.75 eV. We find that the transient carrier dynamics in Au-UNWs under extreme excitation regime is slower than predicted by the often used two-temperature model. Systematically probing the dynamics by varying the pump intensity from weak to strong excitation regime reveals that the mechanism of carrier relaxation through electron-phonon observed so far in larger size Au nanostructures is not sufficient in the Au-UNWs. We show that the reduced screening of e-e interaction due to spilling of conduction band and localization of core (d band) electrons at the surface promotes Auger heating.