arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1803.00547cond-mat.mes-hall
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纳米单晶表面等离子体共振本征手性的观测

Observation of intrinsic chirality of surface plasmon resonances in single nanocrystals

Jong-Won Park

摘要:

基于分子光学活性的量子力学理论,中心对称金属晶体中的表面等离子体被认为是非手性的。单电子理论不足以描述晶体中的光学活性,其中偏振态沿光传播方向的空间变化在超过分子的尺寸中至关重要。这种空间色散可以极大地改变等离子体纳米晶体中的光学近场,但尚未在纳米尺度上得到实验证明。在这里,自然的圆二色性的表面等离子体在球形金,银,铜纳米晶体在溶液中的实验观察。它起源于光学区域中小至5纳米的尺寸处发生的空间色散(非局域性)。特别地,电磁压力或纵向体积等离子体激元导致入射光的横向电场的相移和偏振旋转。偶极表面等离子体表现出负椭圆率和相应的电场负相移(即,光学左手),而四极表面等离子体在椭圆率和相移方面都具有正号(即,光学右手)。结构的影响,如电子束组装,电子束的形状,电子自旋极化,等离子体分子相互作用的访问。体等离子体激元内的带间跃迁也产生一个积极的旋转强度。这项研究暗示了各向同性纳米晶体中平行于波矢的轴向偏振的光学破缺,这将影响传导电子动力学,热电子产生,等离子体纳米晶体表面的非线性光学响应以及束缚d带电子的光学激发。

英文摘要:

Surface plasmons in a centrosymmetric metal nanocrystal have been perceived as achiral, based on the quantum-mechanical theory of molecular optical activity. The one-electron theory is insufficient to describe optical activity in crystals, where spatial variation of polarization states along the light propagation direction is crucial in dimensions exceeding molecules. Such spatial-dispersion, which can drastically modify the optical near-field in plasmonic nanocrystals, has yet to be experimentally proved at the nanometer scale. Here, the experimental observation of natural circular dichroism of surface plasmons in spherical gold, silver, and copper nanocrystals in solution is presented. It originates from spatial dispersion (nonlocality) occurred at a dimension as small as 5 nanometers in the optical region. In particular, the electromagnetic pressure or longitudinal volume plasmons result in phase-shift and polarization rotation of the transverse electric field of incident light. Dipolar surface plasmons exhibit negative ellipticity and corresponding negative phase-shift of the electric field (i.e., optically left-handed), whereas quadrupolar surface plasmons have positive signs in both ellipticity and phase-shift (i.e., optically right-handed). Structural effects such as nanocrystal assembly, nanocrystal shape, electron spin-polarization, and plasmon-molecule interaction are accessed. Volume plasmons inside the nanocrystal also produce a positive rotational strength for the interband transition. This study implicates optical symmetry-breaking in isotropic nanocrystals by the axial polarization parallel to the wavevector, which will impact on conduction electron dynamics, hot-electron generation, and nonlinear optical response at the surface of plasmonic nanocrystals as well as optical excitation of bound d-band electrons.

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