Giant tunable nonreciprocity of light in Weyl semimetals

Abstract

The propagation of light in Weyl semimetal films is analyzed. The magnetic family of these materials is known by anomalous Hall effect, which, being enhanced by the large Berry curvature, allows one to create strong gyrotropic and nonreciprocity effects without external magnetic field. The existence of nonreciprocal waveguide electromagnetic modes in ferromagnetic Weyl semimetal films in the Voigt configuration is predicted. Thanks to the strong dielectric response caused by the gapless Weyl spectrum and the large Berry curvature, ferromagnetic Weyl semimetals combine the best waveguide properties of magnetic dielectrics or semiconductors with strong anomalous Hall effect in ferromagnets. The magnitude of the nonreciprocity depends both on the internal Weyl semimetal properties, the separation of Weyl nodes, and the external factor, the optical contrast between the media surrounding the film. By tuning the Fermi level in Weyl semimetals, one can vary the operation frequencies of the waveguide modes in THz and mid-IR ranges. Our findings pave the way to the design of compact, tunable, and effective nonreciprocal optical elements. arXiv:1808.00342v3 [cond-mat.mes-hall]

Axion-Field-Enabled Nonreciprocal Thermal Radiation in Weyl Semimetals

“…We show that the nonreciprocal thermal properties are highly temperature dependent because of the strong temperature dependence of the chemical potential. Although the nonreciprocal optical response of a magnetic Weyl semimetal is already predicted [15], its implication in thermal radiation has not been explored before.…”

“…Following Ref. [ 15], in this work, we use the parameters ε b = 6.2, ξ c = 3, τ = 1000 fs, g = 2, and v F = 0.83×10 5 m/s. We choose the chemical potential to be E F = 0.15 eV at T = 300 K, which is typical for doped Weyl semimetals.…”

Large nonreciprocal absorption and emission of radiation in type-I Weyl semimetals with time reversal symmetry breaking

“…The large anomalous Hall angle can be a key to achieve large non-reciprocal optical response since the energy difference of the two surface plasmon modes with opposite propagation direction, as we will discuss more in this work, is proportional to the ratio of off-diagonal to diagonal elements of the dielectric tensor, which can be interpreted as the anomalous Hall angle at finite frequency. Therefore, the large Hall angle of Weyl semimetals is expected to be large even at finite frequency and can create large non-reciprocal wave propagation 32 .…”

“…Several models of the dielectric tensor of type-I Weyl semimetals have been proposed. The approach in 32,33 is based on the constitutive relation of the electric displacement field that includes two additional terms describing the anomalous Hall current and the chiral magnetic effect, both of which contribute to off-diagonal elements of the dielectric tensor 33,34 . Both effects are the manifestations of the chiral anomaly, i.e., non-conservation of the chiral current, and are described by the axion term in the electromagnetic field action 35 .…”

Optical Hall effect and gyrotropy of surface polaritons in Weyl semimetals

“…A number of recent studies have suggested that Weyl semimetals (WSMs) should have highly unusual optical response originated from unique topological properties of their bulk and surface electron states; see e.g. [1][2][3][4][5][6][7][8][9][10][11][12][13] and references therein. Their optical response can be used to provide detailed spectroscopic information about their electronic structure which could be difficult to obtain by any other means.…”