Brey Luis, Stauber T, Slipchenko T, Martín-Moreno L
Materials Science Factory, Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco, 28049 Madrid, Spain.
Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza, Zaragoza 50009, Spain and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, Zaragoza 50009, Spain.
Phys Rev Lett. 2020 Dec 18;125(25):256804. doi: 10.1103/PhysRevLett.125.256804.
We discuss plasmons of biased twisted bilayer graphene when the Fermi level lies inside the gap. The collective excitations are a network of chiral edge plasmons (CEP) entirely composed of excitations in the topological electronic edge states that appear at the AB-BA interfaces. The CEP form a hexagonal network with a unique energy scale ε_{p}=(e^{2})/(ε_{0}εt_{0}) with t_{0} the moiré lattice constant and ε the dielectric constant. From the dielectric matrix we obtain the plasmon spectra that has two main characteristics: (i) a diverging density of states at zero energy, and (ii) the presence of a plasmonic Dirac cone at ℏω∼ε_{p}/2 with sound velocity v_{D}=0.0075c, which is formed by zigzag and armchair current oscillations. A network model reveals that the antisymmetry of the plasmon bands implies that CEP scatter at the hexagon vertices maximally in the deflected chiral outgoing directions, with a current ratio of 4/9 into each of the deflected directions and 1/9 into the forward one. We show that scanning near-field microscopy should be able to observe the predicted plasmonic Dirac cone and its broken symmetry phases.
当费米能级位于能隙内时，我们讨论了偏置扭曲双层石墨烯的等离激元。集体激发是一个手性边缘等离激元（CEP）网络，完全由出现在AB - BA界面处的拓扑电子边缘态中的激发构成。CEP形成一个具有独特能量尺度ε_{p}=(e^{2})/(ε_{0}εt_{0})的六边形网络，其中t_{0}是莫尔晶格常数，ε是介电常数。从介电矩阵中我们得到了等离激元光谱，它有两个主要特征：（i）零能量处态密度发散，以及（ii）在ℏω∼ε_{p}/2处存在一个等离激元狄拉克锥，其声速v_{D}=0.0075c，它由锯齿形和扶手椅形电流振荡形成。一个网络模型表明，等离激元能带的反对称性意味着CEP在六边形顶点处最大程度地向偏转的手性出射方向散射，每个偏转方向的电流比为4/9，向前方向的电流比为1/9。我们表明，扫描近场显微镜应该能够观察到预测的等离激元狄拉克锥及其对称性破缺相。
