低温表面等离激元基本物理问题研究

The high loss associated with surface plasmons is one of the key issues that limit the development of plasmonics. The losses can be radiative or nonradiative. The nonradiative one comes from the Ohmic losses of the conduction electrons in the metal, which originates from electron-phonon scattering, electron-electron scattering and electron-surface/defects collisions. The electron-phonon scattering is temperature dependent. However, the temperature dependence of the resistance for metals is well-known. For crystallized novel metals, the resistance drops significantly at low temperature. There is few studies on the low temperature measurement on surface plasmons. Most of them concluded that the effect of temperature is not as significant. So what is reason for the disagreement between the two measurements? Interband transition? Size effect? What is the limit of the loss of surface plasmons at low temperature? Is there some specific regions at which the loss can be very small? We will measure the loss of surface plasmons at low temperature and answer the above questions. This topic is of importance value to the field of plasmonics.

表面等离激元的高损耗是制约表面等离激元光学领域发展的重要因素之一。损耗可分为辐射损耗和非辐射损耗。其中，非辐射损耗来自金属内部电子的欧姆损耗，具体包括电子-声子散射、电子-电子散射、电子-界面/缺陷散射。其中电子-声子散射与温度有关。然而，金属电阻随温度的变化关系已经是广为人知的规律，特别是单晶贵金属（金或银）低温下电阻可显著降低。国际上虽有少数关于表面等离激元低温的测量，但普遍得到的结论是温度影响存在却并不显著。那么是什么原因导致两者不一致，带间跃迁？尺寸效应？表面等离激元损耗的低温极限耗是多少？是否在特定的范围内、某种结构上损耗可以非常低？本项目将通过测量低温下金属纳米结构表面等离激元的损耗，结合理论分析得到低温极限性能，回答上述几个基本物理问题。这对表面等离激元光学领域具有参考价值。

表面等离激元的高损耗是制约表面等离激元光学领域纵深发展的关键因素。理解等离激元的耗散机制及其随温度、结构尺寸、形貌、光学模式种类等参数的变化规律是利用等离激元优异特性和设计高品质等离激元器件的基础。本项目通过对不同温度下等离激元耗散通道的测量，建模得到电子-声子散射、电子-电子散射、电子-界面/缺陷散射以及辐射衰减等耗散机制的相对贡献大小；通过不同温度下单颗粒暗场散射技术证实等离激元纳腔的超灵敏特性，获得亚皮米精度的厚度变化传感，发展定量表面增强拉曼光谱测量等离激元量子极限场增强等基本物理问题；最后通过发展室温纳腔量子光学，探讨无需低温的表面等离激元-激子相互作用，实现室温下二维过渡金属卤族化合物激子圆偏振度的大幅提升以及Rabi劈裂，实现纳腔中飞秒超快衰减速率的测量，以及室温下高度定向分发的拉曼信号。其中，通过温度控制纳腔的热胀冷缩使得间隙厚度和折射率的极微弱变化，实现亚皮米精度的厚度变化的传感，这大幅提升了原有表面等离激元“尺子”的分辨率，可望在原位微弱物理/化学量的传感方面有重要应用价值。项目所发展的室温纳腔光物理，可望在超快发光、光开光与光调制方面取得重要应用。