Optical absorption in 3D topological insulator Bi2Te3 with applications to THz detectors (Presentation Recording)

Parijat Sengupta; Enrico Bellotti

doi:10.1117/12.2190356

5 October 2015 Optical absorption in 3D topological insulator Bi₂Te₃ with applications to THz detectors (Presentation Recording)

Parijat Sengupta, Enrico Bellotti

Author Affiliations +

Proceedings Volume 9555, Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications; 95550F (2015) https://doi.org/10.1117/12.2190356
Event: SPIE Nanoscience + Engineering, 2015, San Diego, California, United States

Abstract

Topological insulators (TI) are a new class of materials that have an energy gap in bulk but possess gapless states bound to the sample surface or edge that have been theoretically predicted and experimentally observed [1]. The topological state in Bi2Te3 is characterized by a linear dispersion and a Dirac cone at the Γpoint. The optical absorption on the surface of a TI is given by the standard graphene-like απ/2 when a linear dispersion is assumed. Realistically, at k-points away from Γ, higher order cubic terms in k that represent the underlying hexagonal symmetry [2] of the crystal dominate and give rise to warping of bands. The optical absorption of a ferromagnetic coated gapped 3D TI film with warping terms considered is longer απ/2 but significantly modified. We demonstrate, by using wave functions from a continuum-Hamiltonian and Fermi-golden rule, the absorption spectrum on the surface of a TI as a function of the chemical potential, film-thickness and incident photon energy. A linear response theory based calculation is also performed using the Kubo formula to determine the longitudinal optical conductivity whose real part gives absorption as a function of photon frequency. The absorption in materials with Dirac fermions which is significantly higher than in normal THz detectors [3] can be further modulated in a TI by explicitly including the warping term making them highly efficient and tunable photodetectors. [1] M.Hasan and C.Kane, Rev.Mod.Phys. 82, 3045(2010) [2] L.Fu, Phys.Rev.Lett.103, 266801(2009) [3] X.Zhang et al., Phys. Rev B, 82, 245107(2010)

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Parijat Sengupta and Enrico Bellotti "Optical absorption in 3D topological insulator Bi₂Te₃ with applications to THz detectors (Presentation Recording)", Proc. SPIE 9555, Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications, 95550F (5 October 2015); https://doi.org/10.1117/12.2190356

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KEYWORDS

Absorption

Sensors

Terahertz radiation

Dispersion

Crystals

Fermions

Ferromagnetics

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