Optical response in subnanometer hollow sodium nanowires

We simulate and analyze the influence of nonlocal effects on the optical properties of thin metal hollow nanowires by finite element method. Nonlocal effects in hollow nanowires with both nm-sized overall volume and a tiny metal shell are considerable for extinction cross section but more for field enhancement, resulting in nonlocal plasmonic modes excited. Then, we show the dependence of extinction effects of a hollow super-nanowire on its parameters, including the metal shell thickness, the average radius and the optical constant of the hollow core. We find that nonlocal quadrupolar mode is very sensitive to the thickness of metal layer but with great stability as increasing the hollow nanowire dimension or changing the hollow core. Furthermore, the eccentricity of the hollow nanowire brings out new physical phenomena, such as nanofocusing and multimodes. The proposed structure promises a great of applications in nanoscale, such as designing nanoplasmonic antenna, sensing and nonlinear optics, etc.