Electromagnetic scattering by spheres of topological insulators

• The scattering coefficients for TI spheres are derived analytically.
• Strong backward scattering are found in both Rayleigh and Mie scattering regimes.
• These backward scattering are caused by topological magneto-electric effect.
• Anti-resonances are studied for cross-polarized scattering coefficients.
• Field trapping effect is revealed at the anti-resonances.

The electromagnetic scattering properties of topological insulator (TI) spheres are systematically studied in this paper. Unconventional backward scattering resulting from the topological magnetoelectric (TME) effect are found in both Rayleigh and Mie scattering regimes. This enhanced backward scattering can be realized by introducing an impedance-matched background. In addition to conventional resonances, interesting antiresonances in scattering coefficients are found in the Mie scattering regime. At the antiresonances, electric or magnetic fields induced by the TME effect can be completely trapped inside TI spheres. In the Rayleigh limit, a method to determine the quantized TME effect of TIs is proposed simply based on the measured electric field components of scattered waves in the far field.