Broadband strong optical dichroism in topological Dirac semimetals with Fermi velocity anisotropy*

Abstract

Prototypical three-dimensional (3D) topological Dirac semimetals (DSMs), such as Cd3As2 and Na3Bi, contain electrons that obey a linear momentum–energy dispersion with different Fermi velocities along the three orthogonal momentum dimensions. Despite being extensively studied in recent years, the inherent Fermi velocity anisotropy has often been neglected in the theoretical and numerical studies of 3D DSMs. Although this omission does not qualitatively alter the physics of light-driven massless quasiparticles in 3D DSMs, it does quantitatively change the optical coefficients which can lead to nontrivial implications in terms of nanophotonics and plasmonics applications. Here we study the linear optical response of 3D DSMs for general Fermi velocity values along each direction. Although the signature conductivity-frequency scaling, σ(ω) ∝ ω, of 3D Dirac fermion is well-protected from the Fermi velocity anisotropy, the linear optical response exhibits strong linear dichroism as captured by the universal extinction ratio scaling law, Λij = (vi /vj )2 (where i ≠ j denotes the three spatial coordinates x,y,z, and vi is the i-direction Fermi velocity), which is independent of frequency, temperature, doping, and carrier scattering lifetime. For Cd3As2 and Na3Bi3, an exceptionally strong extinction ratio larger than 15 and covering a broad terahertz window is revealed. Our findings shed new light on the role of Fermi velocity anisotropy in the optical response of Dirac semimetals and open up novel polarization-sensitive functionalities, such as photodetection and light modulation.

Evidence of 3D Dirac conical bands in TlBiSSe by optical and magneto-optical spectroscopy

“…For this purpose, we will use the DC anisotropy resistivity ratio, and optical and magneto-optical measurements performed on sample S 3 . The real part of the optical conductivity of an anisotropic 3D Dirac system [38][39][40] for incoming photon frequency ω and with an electric field pointing in the x-direction…”

Analogous Black Holes in Type-III Dirac Semimetal Ni3In2X2 (X = S, Se)

“…In order to calculate the total conductivity of a metal the Kubo-Greenword formula can be utilized, since the transverse conductivity vanishes, only the diagonal terms of the equation remain. The total conductivity σ ii composes from two components σ intra ii and σ inter ii [63,64].…”

Topological states in boron phosphide with zinc-blende structure

“…Topological electronic materials have been one of the most active research fields in the past decade. To this date, many types of topological electronic materials (Wang, 2008;Li et al, 2009;Hasan and Kane, 2010;Moore, 2010;Qi and Zhang, 2011;Gao et al, 2016;Tokura et al, 2019;Wang et al, 2020a;Yue et al, 2020), including topological insulators (Hasan and Kane, 2010;Moore, 2010;Qi and Zhang, 2011;Tokura et al, 2019), spingapless semiconductors (Wang, 2008;Li et al, 2009;Gao et al, 2016;He et al, 2017;Wang et al, 2020a;Yue et al, 2020;Yang et al, 2021), topological semimetals (Vazifeh and Franz, 2013;Yang et al, 2015;Chang et al, 2016;Liu et al, 2019a;Wang et al, 2020b;Lim et al, 2020;Liu et al, 2022a), (Li et al, 2020b;Li et al, 2020c;Li et al, 2020d), and topological superconducting (Chung et al, 2011;Stoudenmire et al, 2011;Sato and Ando, 2017;Zhang et al, 2018;Frolov et al, 2020), have been predicted in theory; some of them are also confirmed in experiments. For example, some three-dimensional (3D) material databases documented tens of thousands of candidates as topological semimetals.…”