Abstract
We investigated magneto-optical response of undoped Bi2Te3 films in the terahertz frequency range (0.3–5.1 THz, 10–170 cm−1) in magnetic fields up to 10 T. The optical transmission, measured in the Faraday geometry, is dominated by a broad Lorentzian-shaped mode, whose central frequency linearly increases with applied field. In zero field, the Lorentzian is centered at zero frequency, representing hence the free-carrier Drude response. We interpret the mode as a cyclotron resonance (CR) of free carriers in Bi2Te3. Because the mode’s frequency position follows a linear magnetic-field dependence and because undoped Bi2Te3 is known to possess appreciable number of bulk carriers, we associate the mode with a bulk CR. In addition, the cyclotron mass obtained from our measurements fits well the literature data on the bulk effective mass in Bi2Te3. Interestingly, the width of the CR mode demonstrates a behavior non-monotonous in field. We propose that the CR width is defined by two competing factors: impurity scattering, which rate decreases in increasing field, and electron-phonon scattering, which exhibits the opposite behavior.
Highlights
IntroductionFrom the theory point of view, a three-dimensional (3D) topological insulator (TI) possesses insulating bulk and conducting surfaces, the conduction channels at surfaces being spin-polarized [1,2,3,4]
From the theory point of view, a three-dimensional (3D) topological insulator (TI) possesses insulating bulk and conducting surfaces, the conduction channels at surfaces being spin-polarized [1,2,3,4].Since the spin polarization can potentially be utilized in spintronic devices, topological insulators have attracted a lot of attention in the past years [5,6]
We used binary Bi2 Te3 and elemental Te. This is different from the standard practice, when elemental (Bi and Te) sources are utilized with the typical flux ratio of Te/Bi being about 10 to 20
Summary
From the theory point of view, a three-dimensional (3D) topological insulator (TI) possesses insulating bulk and conducting surfaces, the conduction channels at surfaces being spin-polarized [1,2,3,4]. Since the spin polarization can potentially be utilized in spintronic devices, topological insulators have attracted a lot of attention in the past years [5,6]. The real samples of 3D topological insulators often conduct on their surfaces, and in the bulk. Considerable efforts have been made to understand and separate the properties of surface and bulk charge carriers. These properties can be studied via different spectroscopic techniques, such as angle-resolved photoemission spectroscopy (ARPES) or optical and magneto-optical spectroscopy.
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