Sellati Niccolò, Fiore Jacopo, Castellani Claudio, Benfatto Lara
Department of Physics and ISC-CNR, "Sapienza" University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy.
Nanomaterials (Basel). 2024 Jun 13;14(12):1021. doi: 10.3390/nano14121021.
Electromagnetic waves propagating in a layered superconductor with arbitrary momentum, with respect to the main crystallographic directions, exhibit an unavoidable mixing between longitudinal and transverse degrees of freedom. Here we show that this basic physical mechanism explains the emergence of a well-defined absorption peak in the in-plane optical conductivity when light propagates at small tilting angles relative to the stacking direction in layered cuprates. More specifically, we show that this peak, often interpreted as a spurious leakage of the -axis Josephson plasmon, is instead a signature of the true longitudinal plasma mode occurring at larger momenta. By combining a classical approach based on Maxwell's equations with a full quantum derivation of the plasma modes based on modeling the superconducting phase degrees of freedom, we provide an analytical expression for the absorption peak as a function of the tilting angle and light polarization. We suggest that an all-optical measurement in tilted geometry can be used as an alternative way to access plasma-wave dispersion, usually measured by means of large-momenta scattering techniques like resonant inelastic X-ray scattering (RIXS) or electron energy loss spectroscopy (EELS).
在具有任意动量的层状超导体中传播的电磁波，相对于主要晶体学方向，会在纵向和横向自由度之间表现出不可避免的混合。在此我们表明，这种基本物理机制解释了当光在层状铜酸盐中相对于堆叠方向以小倾斜角传播时，面内光导率中明确吸收峰的出现。更具体地说，我们表明这个通常被解释为 c 轴约瑟夫森等离子体激元的虚假泄漏的峰，实际上是在更大动量下出现的真实纵向等离子体模式的特征。通过将基于麦克斯韦方程组的经典方法与基于对超导相位自由度建模的等离子体模式的完全量子推导相结合，我们给出了作为倾斜角和光偏振函数的吸收峰的解析表达式。我们建议在倾斜几何结构中的全光测量可以用作获取等离子体波色散的替代方法，等离子体波色散通常通过诸如共振非弹性 X 射线散射（RIXS）或电子能量损失谱（EELS）等大动量散射技术来测量。
