Signatures of charge inhomogeneities in the infrared spectra of topological insulators Bi₂Se₃, Bi₂Te₃ and Sb₂Te₃

Abstract

We present the results of an infrared spectroscopy study of topological insulators Bi(2)Se(3), Bi(2)Te(3) and Sb(2)Te(3). Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi(2)Se(3), whereas in Bi(2)Te(3) and Sb(2)Te(3) it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature.

Fanoq-reversal in topological insulator Bi2Se3

“…We also estimate carrier mobility in our sample µ=ω c /(B γ)= 1800 cm −2 /Vs, which is almost a factor of 2 smaller compared with the value obtained on the thin film [8]. However, our value is comparable with the values obtained from Hall measurements [3] on bulk Bi 2 Se 3 samples with similar carrier density [18], and almost a factor of 2 greater compared with the thick film [16]. Fig.…”

“…We choose to display ω q instead of q, because for fields around 10 Tesla, q acquires large values (theoretically it diverges), which renders the fitting unstable. As the plot indicates, ω q starts as negative [2,18] for zero and small fields, but around 10 Tesla changes sign and becomes positive. This effect is referred to as the q-reversal.…”

“…The cyclotron resonance in Bi 2 Se 3 has so far been observed only in thin films [8,16]. [18], the most prominent feature in reflectance is the plasma edge located at approximately 180 cm −1 . In addition, two optically active phonon modes, observed previously [3,2,14], are detected in the form of dips located at approximately 60 cm −1 and 130 cm −1 .…”

“…These three modes are: 1) a Drude mode, which in magnetic field shifts to finite frequencies and becomes a cyclotron resonance, 2) a phonon mode at 60 cm −1 , which has been known to be asymmetric [2,18], and 3) a phonon mode at 130 cm −1 which does not have significant asymmetry and is modeled as a Lorentzian [18]. The cyclotron mode was modeled with Eq.…”

Спектры отражения кристаллов p-Bi-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=- : Sn в широкой ИК области

“…Значительное количество информации о свойствах электронной подсистемы кристаллов p-Вi 2 Те 3 было по-лучено из анализа спектров отражения [1,[6][7][8][9][10][11][12][13]. Однако найденные из этих спектров параметры плазменных колебаний, так же как в случае кинетических явлений, характеризуются значительным разбросом их величин.…”