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arXiv 2303.07413quant-phphysics.optics
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Dirac例外点及其等谱厄米特对应点的分析

Analysis of Dirac exceptional points and their isospectral Hermitian counterparts

Jose H. D. Rivero, Liang Feng, Li Ge

摘要:

最近,在一个非厄米特系统中发现了一个Dirac例外点。与厄米特系统中的狄拉克点不同,这个狄拉克EP除了简并能量之外还合并了本征态。也不同于典型的EP,在这个狄拉克EP连接的两个能级在其附近仍然是真实的,并显示线性而不是平方根色散,形成一个倾斜的狄拉克锥的混合空间组成的动量维和合成维的强度的非厄米性。在这份报告中,我们首先提出了简单的三带和两带矩阵模型与狄拉克EP,其中的线性色散的倾斜狄拉克锥可以解析地表示。重要的是,我们的分析还表明,存在厄米和非厄米系统,在其整个参数空间中具有相同的(实值)能量谱,除了前者中的一个或多个简并被后者中的狄拉克EP所取代。最后,我们证明了存在一个假想的狄拉克锥与EP在其中心。

英文摘要:

Recently, a Dirac exceptional point (EP) was reported in a non-Hermitian system. Unlike a Dirac point in Hermitian systems, this Dirac EP has coalesced eigenstates in addition to the degenerate energy. Also different from a typical EP, the two energy levels connected at this Dirac EP remain real in its vicinity and display a linear instead of square root dispersion, forming a tilted Dirac cone in the hybrid space consisting of a momentum dimension and a synthetic dimension for the strength of non-Hermiticity. In this report, we first present simple three-band and two-band matrix models with a Dirac EP, where the linear dispersion of the tilted Dirac cone can be expressed analytically. Importantly, our analysis also reveals that there exist Hermitian and non-Hermitian systems that have the same (real-valued) energy spectrum in their entire parameter space, with the exception that one or more degeneracies in the former are replaced by Dirac EPs in the later. Finally, we show the existence of an imaginary Dirac cone with an EP at its center.

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