Exploring Spectral Singularities in Dirac Semimetals: The Role of Non-Hermitian Physics and Dichroism

Abstract

In this study, motivated by recent advancements in non-Hermitian physics, we explore new characteristics of Dirac semimetals (DSMs) using the spectral singularities by means of scattering techniques, with the goal of uncovering additional unique properties. To achieve this, we investigate how the axion texture of a DSM affects its topological properties by analyzing its interaction with electromagnetic waves. We examine the transverse electric (TE) mode configuration, where the magneto-electric effect induces a dichroic property in these materials. This behavior is particularly interesting and commonly seen in potential DSM candidates. Consequently, we report for the first time that a dichroic DSM generates 12 unique topological laser types. We discover that surface currents are generated by topological terms on the surface of the DSM slab. Furthermore, we examine how the θ term associated with axions in topological materials contributes to these topological properties. Our study reveals distinct topological role of the θ term more clearly than ever before. Our results confirm that the topological properties of DSMs with a single Dirac cone remain stable under external influences and that a topologically robust DSM laser can be developed accordingly

Figures (9)

• Figure 1: TE mode configuration for the interaction of electromagnetic wave incident by an angle $\phi$ measured from the normal to the surface of DSM slab. Left panel displays the 3D configuration while middle panel shows the top view. Red dot identifies the single Weyl node. $\theta$ terms corresponding to each medium are demonstrated on the right panel. Colored region specifies the DSM.
• Figure 2: The frequency-dependent real and imaginary parts of the conductivity for Na$_3$Bi. The conductivity at 10 THz frequency is indicated by $\sigma_0$.
• Figure 3: The spectral singularity configurations and laser output modes of the Plus-Mode (left panel), Minus-Mode (middle panel) and Bimodal case (right panel) in a DSM medium. Waves with amplitudes $B_{1+}$ and $A_{3+}$ are output from the left and right sides in the Plus-Mode, amplitudes $B_{1-}$ and $A_{3-}$ are for the Minus-Mode, and amplitudes $B_{1+}$, $B_{1-}$, $A_{3+}$, and $A_{3-}$ are for the Bimodal case, respectively.
• Figure 4: A diagram of topological DSM laser types within the components of the transfer matrix for a DSM environment. It illustrates the laser generation conditions for each topological DSM laser type listed in Table \ref{['table3']}, with different colors representing different laser types. Notably, only the second and fourth columns of the transfer matrix generate laser beams.
• Figure 5: The spectral singularities are displayed over the $\lambda - g$ parameters of the Plus Mode configuration. Panels (a), (b) and (c) show the real zero values of components of the transfer matrix separately, while intersection points of these points are shown in panel (d). Graphs are plotted using the data obtained from Eq. (\ref{['specifications']}).