Thermal coherence properties of topological insulator slabs in time-reversal symmetry breaking fields

Abstract

We first develop a general Green's-function method for the slab geometry, which can handle quite complex conversions between the different polarized radiation modes. Then by using the method, we study the near field thermal coherence properties of a slab of Z 2 topological insulator (TI) with a finite thickness. Under a strong enough external magnetic field, the gapless helical Dirac fermions on the TI surfaces can acquire an energy gap larger than the photon energy of the radiation field at the Dirac point. This gapped surface states can couple strongly with the waveguide modes in the bulk of the TI slab, which thus induces an electromagnetic resonance. Exactly due to the resonance, the coherence properties of the thermal radiation field can be modified dramatically. For Z 2 topological insulators, the parameter regime with the surface Hall conductivity half integer quantized is unique. We demonstrated that within the parameter regime, for a TI slab of a proper thickness, the thermal radiation energy density can be enhanced very much, and the coherence length of the thermal radiation field can be as long as twice that of SiC.

Optical conductivities and signatures of topological insulators with hexagonal warping

“…By considering the zero-warping limit (γ → 0), we can recover the results for a TI with no warping effect: 13,15 Re σ…”

“…13,15 The contribution of the interband processes to the optical Hall conductivity has a similar mathematical structure, and we can obtain their explicit expressions by following similar procedures as above. However, one may have to pay attention to the product of expectations of the velocity operators:…”

“…13,15 Similarly, the contribution from the intraband processes to the optical Hall conductivity σ xx (ω) is given by…”

“…The magnetoelectric coupling is the origin of many interesting phenomena proposed recently, such as the possibility of inducing magnetic monopoles, 12 the giant magneto-optical Kerr effect, 13 the tunable Casimir effect, 14 and the enhancement of the spatial coherence of the thermal radiation field. 15 A recent angle-resolved photoemission experiment for Bi 2 Te 3 16 has revealed that the equal-energy contour would be distorted from the well-known circle shape of the Dirac cone when the equal-energy contour has a large energy difference (i.e., ∼0.1 eV) from the Dirac point. Such geometrical distortion of the equal-energy contour is viewed as the consequence of a crystal and time-reversal-symmetry-constrained hexagonal warping term.…”

Unusual electromagnetic scattering by cylinders of topological insulator

“…An additional term in the Maxwell Lagrangian, ΔL = (θ α/4π 2 )E • B, is introduced to describe the TME effect [3,4], where α = e 2 /hc is the fine structure constant, θ = (2p + 1)π is the quantized axion angle [4] with p being an integer, and E and B are the electric field and magnetic induction, respectively. The TME effect plays a key role in the electromagnetic (EM) responses of TIs and many unconventional optical phenomena due to the TME effect have been found [5][6][7][8][9][10][11].…”