Giant optical activity and Kerr effect in type-I and type-II Weyl semimetals

Abstract

We explore optical activity in thin films and bulk of type-I and type-II Weyl semimetals (WSM), and demonstrate the existence of a giant Kerr effect in both. In time-reversal symmetry broken WSM thin films, the polarization rotation is caused by the optical Hall conductivity including the anomalous Hall term. The Kerr angle is found to be ∝ Q/ω, with Q and ω being the Weyl node separation and the optical frequency, respectively. In contrast, the optical activity in the bulk WSM is dominated by axion electrodynamics, which persists even in the Pauli blocked regime of no optical transitions. In bulk WSM, Q acts analogous to the magnetization in magnetic materials, leading to large 'polar Kerr effect' (linear in Q) when light is incident on WSM surface without Fermi arc states, and the 'Voigt effect' (quadratic in Q), when light is incident on surface with Fermi arc states.arXiv:1903.08590v1 [cond-mat.mes-hall]

Photonic spin Hall effect on the surfaces of type-I and type-II Weyl semimetals

“…As illustrated in Figure 1A, one bulk WSM contains a pair of oppositely tilted Weyl nodes with broken time reversal symmetry [12,36,37]. These two Weyl nodes with chirality ξ = ± 1 are located in the Brillouin zone at k = {0, 0, ∓Q}.…”

“…These two Weyl nodes with chirality ξ = ± 1 are located in the Brillouin zone at k = {0, 0, ∓Q}. interband optical conductivity of bulk WSM can be written as [12]…”

“…The Weyl nodes in WSMs can be anisotropic and tilted away from the vertical axis [11]. Accordingly, WSMs are classified into type-I (partially tilted) phase with vanishing density of states (DOS) at the Weyl point, and type-II (overtilted) phase with a finite DOS at the Fermi energy and an electron and a hole pocket on either side of the Weyl point [12,13]. To date, ideal type-I Weyl points with symmetric cone spectra have been ascertained in available semimetals (e.g.…”

“…Among the research on topological optics, optical conductivity is a key parameter to control and ameliorate the PSHE occurring at a topological interface [30][31][32][33]. However, most of the previous studies do not involve the effects of tilt of Weyl nodes and chemical potential on the complex optical conductivity matrices of WSMs for all frequency ranges [12,[33][34][35]. Therefore, modifying and/or manipulating the PSHE via controlling the tilt and impurity in WSMs, to the best of our knowledge, have not yet been reported so far.…”

“…In 2019, Sonowal et al analytically derived the complex optical conductivity matrices of type-I and type-II WSMs as functions of the tilt and chemical potential, which opens up the possibility to solely examine the impacts of tilt α t of Weyl nodes and chemical potential μ on the PSHE without using any small angle approximation [12]. Besides, the decisive criterion for a type-II WSM is the direct observation of its tilted band crossing in three directions in the momentum space [18].…”