论文标题
非热模型的带结构上的固定点:带隙中的扩展状态和理想的超光隧道
Fixed points on band structures of non-Hermitian models: Extended states in the bandgap and ideal superluminal tunneling
论文作者
论文摘要
在过去十年中,非热门电子模型中的时空反射对称性(PT对称性)引起了很多关注,主要是因为它确保在开放边界条件下计算出的带状结构与在周期性边界条件下计算的条件相同。电磁(EM)模型中通常是从电子模型借来的PT对称性,也具有极大的兴趣,主要是因为它导致“异常”参数值,以下非列米特运算符具有真实特征值,尽管PT对称不是允许这样的异常参数值的均称对称性。在本文中,我们研究了一维PT对称的非官方EM模型,以引入新颖的概念和现象。我们介绍了“固定点”的带结构概念,该概念在相应的有限结构中导致“双向”反射零,与对具有PT对称性的EM结构的共同信念相反(并且没有P和T对称性)。一些固定点自己表现为我们在频段结构上称其为“频段”中的“扩展状态”,而其他一些固定点是频段结构的“转弯点”。带隙中的扩展状态实际上是众所周知的“连续体中界面状态”的双重,而转折点使我们能够在相应的有限结构中观察到“理想”的高光隧道。通过“理想”的超亮性隧道,我们的意思是,不仅传输系数在宽带宽度上具有几乎均匀的相位,而且传输和反射系数的幅度几乎等于统一和零。
Space-time reflection symmetry (PT symmetry) in non-Hermitian electronic models has drawn much attention over the past decade mainly because it guarantees that the band structures calculated under open boundary conditions be the same as those calculated under periodic boundary conditions. PT symmetry in electromagnetic (EM) models, which are usually borrowed from electronic models, has also been of immense interest mainly because it leads to 'exceptional' parameter values below which non-Hermitian operators have real eigenvalues, although PT symmetry is not the sole symmetry which allows such exceptional parameter values. In this article, we examine one-dimensional PT-symmetric non-Hermitian EM models to introduce novel concepts and phenomena. We introduce the band-structure concept of 'fixed points', which leads to 'bidirectional' reflection zeros in the corresponding finite structures, contrary to a common belief about the EM structures with PT symmetry (and without P and T symmetries). Some of the fixed points manifest themselves as what we name 'extended states in the bandgap' on the band structure while some other fixed points are the 'turning points' of the band structure. The extended states in the band gap are in fact the dual of the well-known 'bound states in the continuum' while the turning points allow us to observe 'ideal' superluminal tunneling in the corresponding finite structures. By 'ideal' superluminal tunneling we mean the case where not only the transmission coefficient has an almost uniform phase over a broad bandwidth but also the magnitudes of the transmission and reflection coefficients are almost equal to unity and zero, respectively, over the bandwidth.