Optical characterization ofBi2Se3in a magnetic field: Infrared evidence for magnetoelectric coupling in a topological insulator material

Abstract

We present an infrared magneto-optical study of the highly thermoelectric narrow-gap semiconductor Bi2Se3. Far-infrared and mid-infrared (IR) reflectance and transmission measurements have been performed in magnetic fields oriented both parallel and perpendicular to the trigonal c axis of this layered material, and supplemented with UV-visible ellipsometry to obtain the optical conductivity σ1(ω). With lowering of temperature we observe narrowing of the Drude conductivity due to reduced quasiparticle scattering, as well as the increase in the absorption edge due to direct electronic transitions. Magnetic fields H c dramatically renormalize and asymmetrically broaden the strongest far-IR optical phonon, indicating interaction of the phonon with the continuum freecarrier spectrum and significant magnetoelectric coupling. For the perpendicular field orientation, electronic absorption is enhanced, and the plasma edge is slightly shifted to higher energies. In both cases the direct transition energy is softened in magnetic field. arXiv:0912.2769v2 [cond-mat.str-el]

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

“…These modes transform as 2 + 2 1 + 2 + 2 1 , where 2 + 2 1 and 2 + 2 1 are, respectively, Raman and infrared-active representations [19]. We note that the bulk optical phonons of Bi2Se3 and Bi2Te3 have been previously measured using Raman [20,26,27,28] and neutron scattering [29], and infrared spectroscopy [19,20,30], Figure 1 shows Raman spectra of Bi2Se3 and Bi2Te3 at various temperatures in the ( ) ̅ ( + ) scattering configuration; note the logarithmic scale. Consistent with previous reports [20,27], the bulk Raman-active modes at 10 K are at 38.5 cm -1 ( 1 ), 75.5 cm -1 ( 1 1 ), 135.8 cm -1…”

Trapping of three-dimensional electrons and transition to two-dimensional transport in the three-dimensional topological insulator Bi2Se3under high pressure

“…Bi 2 Se 3 electronic dielectric function at ambient pressure has been shown to be mainly determined [36,37] by a very intense optical transition at 2 eV, that would correspond to its Penn gap [38], according to the Phillips-van Vechten model [39][40][41] to the square of the plasma frequency. In Figure 6-b we plot (E g ) 3/2 versus (ħ PFC ) 2 .…”

“…Concerning the increase of the electronic dielectric constant, let's first try to identify the electronic transitions corresponding to the Penn gap (dielectric function peak at 2 eV) [36,37]. For optical transitions between the valence and conduction band, the only area of the band structure that could give rise to a high joint density of states at 2 eV seems to be around the -L direction.…”

Two-dimensional surface charge transport in topological insulators

“…54 58 and experiments have begun to investigate the transition between the three-and two-dimensional phases in this material. 59 Bi 2 Se 3 has also been studied in a magnetic field, revealing a magnetoelectric coupling 60 and an oscillatory angular dependence of the magnetoresistance. 61 Sample growth dynamics of Bi 2 Te 3 by means of MBE were monitored by reflection high-energy electron diffraction (RHEED).…”