鈮超穎材料於超導相變邊界的光學性質之研究

Abstract

在光學領域中，超導的影響被認為相當的微弱，因為外加入射光的光子能量大小比庫柏電子對（超導電荷載子）的鍵結能高幾個數量級。藉由研究鈮(Niobium, 低溫超導體)在光學波段的電漿子響應，我們探討具有奈米結構的超導超穎材料與無結構超導體薄膜的隨溫度發生變化的光學性質。我們證明鈮超穎材料共振的位置和強度對於溫度改變具有顯著的依賴(從室溫降到數個的克式溫度)，並在超導相變溫度附近(~9K)具有急劇變化。在單獨的實驗中，測量無結構的鈮膜隨溫度改變的介電常數上被觀察到同樣劇烈的變化。我們的研究結果表明超導性確實影響在光學波段的電漿子行為，且可能在形成超導相變附近的光學介電常數的響應中發揮作用。

Superconductivity is commonly expected to be insignificant in optics, where photon energy is orders of magnitude higher than the binding energy of the Cooper pairs, the superconducting charge carriers. By studying optical range plasmonic response of niobium, a conventional low-temperature superconductor, we investigate the temperature-induced changes in the optical properties of a nanostructured superconducting metamaterial as well as unstructured superconductor film. We demonstrate that both the position and the strength of niobium metamaterial resonances exhibit a pronounced dependence on temperature down to a few Kelvin, with a sharp change in the behavior around the superconducting transition temperature at 9K. Equivalently dramatic changes are also observed in the temperature-dependence of the dielectric constant of unstructured niobium film measured in a separate experiment. Our results show that superconductivity does affect plasmonic behavior at optical frequencies and may play a role in forming the optical dielectric response near the superconducting transition.