The role of dimensionality on the quenching of spin-orbit effects in the optics of gold nanostructures.

By first-principles time-dependent density-functional calculations, we show the relevance of relativistic effects to shape the photoabsorption cross section of small gold clusters (Au(n), n < or = 8, and n = 20) and small nanowires (n < or = 7). The relativistic effects not only dictate the stabilization of planar geometries (as it has already been shown by treating the core electrons relativistically): The spin-orbit coupling also has a strong impact in the absorption spectra (resonances and oscillator strengths). This is especially true for nanowires, where the effect of spin orbit is large and not substantially reduced with the chain length, in contrast to more compact gold clusters where this spin-orbit effect tends to be quenched. These results have far reaching consequences in fields such as electronic transport, where gold nanowires are often used, but where spin-orbit effects are generally disregarded.