Starting from the Dirac equation, the relativistic quantum hydrodynamic equations for Dirac electrons on a surface of a three dimensional-topological insulator (TI) are derived and numerically solved to study the spin plasmons. The surface of the TI is modulated by a perpendicular magnetic field and a pulsed exchange field provided by an array of ferromagnetic insulating (FI) stripes. The collective density and velocity oscillations in the two-dimensional Dirac electron gas are simulated and analyzed. It is shown that in spin plasmons, the collective electron density and momentum are modulated by the spin state. Direct experimental observations of such oscillations are possible at laboratory conditions.
我们研究了正常电介质和拓扑绝缘体之间的平面界面处的表面等离子体激元，其中费米能位于拓扑绝缘体的体隙内，并产生了自由狄拉克电子的二维电荷分布。我们开发的等离子体激元色散的计算方法，使用经典电动力学的框架，与修改后的组成方程，由于霍尔电流的拓扑绝缘体，连同一个Lindhard型描述的二维电荷分布的自由狄拉克电子。对于Bi $_2$ X $_3$二元化合物的代表系统，我们发现与最近的相关工作，修改后的组分方程几乎没有影响的表面等离激元色散，但导致旋转的表面等离激元的界面平面的磁极化。
Chiral edge plasmons in quantum anomalous Hall insulators
Beijing Forestry University（北京林业大学）；Beijing Institute of Technology（北京理工大学）；Chinese Academy of Sciences（中国科学院）；University of Science and Technology of China（中国科学技术大学）
The recent developments in the emerging field of plasmonics in graphene and other Dirac systems are reviewed and a comprehensive introduction to the standard models and techniques is given. In particular, we discuss intrinsic plasmon excitations of single and bilayer graphene via hydrodynamic equations and the random phase approximation, but also comment on double and multilayer structures. Additionally, we address Dirac systems in the retardation limit and also with large spin-orbit coupling including topological insulators. Finally, we summarize basic properties of the charge, current and ph…
Propagation of Surface Plasmon Polaritons in Thin Films of Topological Insulators
研究了表面等离子激元在拓扑绝缘体薄膜中的传播。所考虑的材料是第二代三维拓扑绝缘体Bi $_2$ Se $_3$、Bi $_2$ Te $_3$和Sb $_2$ Te $_3$。色散关系和传播长度的数值估计，考虑到拓扑绝缘体以及基板使用Drude-Lorentz模型的体介电函数的变化。确定了影响传播长度的关键因素，并提出了修改色散关系的方法。对Bi $_2$ Se $_3$的实验数据与理论值之间的明显差异提出了解释。
We use a fully quantum mechanical approach to demonstrate control of plasmonic excitations in prototype models of topological insulators by molecule-scale perturbations. Strongly localized surface plasmons are present in the host systems, arising from the topologically non-trivial single-particle edge states. A numerical evaluation of the RPA equations for the perturbed systems reveals how the positions and the internal electronic structure of the added molecules affect the degeneracy of the locally confined collective excitations, i.e., shifting the plasmonic energies of the host system and c…
We analyze collective excitations in models of two-dimensional topological insulators using the random phase approximation. In a two-dimensional extension of the Su-Schrieffer-Heeger model, edge plasmonic excitations with induced charge-density distributions localized at the boundaries of the system are found in the topologically non-trivial phase, dispersing similarly as one-dimensional bulk plasmons in the conventional Su-Schrieffer-Heeger chain. For two-dimensional bulk collective modes, we reveal regimes of enhanced inter-band wave function correlations, leading to characteristic hardening…
Nonlinear Optical Observation of Coherent Acoustic Dirac Plasmons in Thin-Film Topological Insulators
具有类声线性色散的低能电子集体激发在实验和理论上都得到了广泛的研究。然而，在时域测量中出现的相干声等离子体模式很少观察到由于单粒子连续朗道阻尼。在这里，我们报告的观察相干声学狄拉克等离子体（CADP）模式激发间接（静电）对表面耦合薄膜的拓扑绝缘体Bi 2 Se 3。使用瞬态二次谐波发生，一种能够独立监测膜中的面内和面外电子动力学的技术，观察到GHz范围的振荡，而没有相应的瞬态反射率振荡。这些振荡被分配到由倏逝引导兰姆声波引起的横向磁和横向电引导CADP模式，并且由于相对表面狄拉克状态之间的费米子隧穿而保持朗道无阻尼。
Laser-driven parametric instability and generation of entangled photon-plasmon states in graphene and topological insulators
我们表明，一个强的红外激光束倾斜入射到石墨烯可以经历一个参数不稳定性衰减成低频（闲频）光子和太赫兹表面等离子体。这种不稳定性是由于石墨烯的空间色散引起的强烈的面内二阶非线性响应。参量衰减导致THz等离子体激元的有效产生，并引起闲频光子和表面等离子体激元态的量子纠缠。类似的过程可以由拓扑绝缘体如Bi $_2$ Se $_3$的表面态支持。
Control of 2D plasmons in the topological insulator Bi2Se3 with highly crystalline C60 overlayers
University of Glasgow（格拉斯哥大学）；Tyndall National Institute（廷德尔国家研究所）；University of Leeds（利兹大学）；SuperSTEM, SciTech Daresbury Science and Innovation Campus（超级扫描电子显微镜站，达尔斯伯里科学与技术创新园区）；University College Cork（科克大学学院）
The dispersion law of plasmons running along thin wires with radius $a$ is known to be practically linear. We show that in a wire with a dielectric constant $κ$ much larger than that of its environment $κ_e$, such dispersion law crosses over to a dispersionless three-dimensional-like law when the plasmon wavelength becomes shorter than the length $(a/2) \sqrt{(κ/κ_e)\ln(κ/2κ_e)}$ at which the electric field lines of a point charge exit from the wire to the environment. This happens both in trivial semiconductor wires and wires of three-dimensional topological insulators.
An accurate description of the optical response of subwavelength metallic particles and nanogap structures is a key problem of plasmonics. Quantum hydrodynamic theory (QHT) has emerged as a powerful method to calculate the optical response of metallic nanoparticles (NPs) since it takes into account nonlocality and spill-out effects. Nevertheless, the absorption spectra of metallic NPs obtained with conventional QHT, i.e., incorporating Thomas-Fermi (TF) and von Weizsäcker (vW) kinetic energy (KE) contributions, can be affected by several spurious resonances at energies higher than the main loc…
Nonlocal optical generation of spin and charge currents on the surface of magnetic insulators using total absorption and surface plasmons
研究了磁性绝缘体（如\tcb{yttrium iron garnet}）表面金属有限单元中由于磁性表面等离子体（MSP）的吸收而产生的非局域自旋和电荷电流。表面等离子体激元完全被金属反射，而\tcb{an} MSP \tcb{can be}吸收了\tcb{due to the absence of backward states}。\tcb{injection of} MSP在平行于波矢量的纵向产生电压，\tcb{with the voltage}与输入功率成比例。如果金属是铁磁体，则自旋电流在纵向方向上也可以是\tcb{induced}。我们的\tcb{results provide a way to improve upon}自旋电子学和自旋波逻辑器件集成电路。
In a recent paper by Lucas and Das Sarma [Physical Review B 97, 115449 (2018)], a solvable model of collective modes in 2D metals was considered in the hydrodynamic regime. In the current work, we generalize the hydrodynamic theory to 3D metals for which the calculation of sound modes in a strongly-coupled quantum Coulomb plasma can be made explicit. The specific theoretical question of interest is how the usual linearly dispersing hydrodynamic sound mode relates to the well-known gapped 3D plasmon collective mode in the presence of long-range Coulomb interaction. We show analytically that bot…
