Optical properties of Bi2Te2Se at ambient and high pressures

Abstract

The temperature dependence of the complex optical properties of the three-dimensional topological insulator Bi2Te2Se is reported for light polarized in the a-b planes at ambient pressure, as well as the effects of pressure at room temperature. This material displays a semiconducting character with a bulk optical gap of Eg 300 meV at 295 K. In addition to the two expected infrared-active vibrations observed in the planes, there is additional fine structure that is attributed to either the removal of degeneracy or the activation of Raman modes due to disorder. A strong impurity band located at 200 cm −1 is also observed. At and just above the optical gap, several interband absorptions are found to show a strong temperature and pressure dependence. As the temperature is lowered these features increase in strength and harden. The application of pressure leads to a very abrupt closing of the gap above 8 GPa, and strongly modifies the interband absorptions in the mid-infrared spectral range. While ab initio calculations fail to predict the collapse of the gap, they do successfully describe the size of the band gap at ambient pressure, and the magnitude and shape of the optical conductivity.

Bi 2 Te 3−x Se x series studied by resistivity and thermopower

“…gap (200-300 meV), bulk conductivity of known bismuth chalcogenides is relatively high and hinders the observation of topological surface states, even in the most compensated compound Bi 2 Te 2 Se [6,7]. Throughout this series, the Fermi level is found either within the conduction or valence band.…”

Interband absorption edge in the topological insulators Bi2(Te1−xSex)3

“…The infrared and optical response of Bi 2 (Te 1−x Se x ) 3 compounds have been intensively studied in order to characterize their vibrational properties 11 , interband absorption [12][13][14][15][16][17] and free charge carrier properties 14,[18][19][20] . Even the surface states [21][22][23][24] and strong Faraday rotation 25 have been observed by infrared spectroscopy.…”

Use of x-ray scattering functions in Kramers-Kronig analysis of reflectance

“…Many reports of Kramers-Kronig analysis of reflectance have appeared, spanning more than 50 years, 7 with studies of metals, [8][9][10][11][12][13][14][15] pure and doped elemental solids, [16][17][18] organic conductors, [19][20][21] charge-density-wave materials, [22][23][24] conducting polymers, [25][26][27] cuprate superconductors, [28][29][30][31][32][33][34][35][36][37][38] manganites, [39][40][41] pnictides, [42][43][44][45][46][47][48] heavy-Fermions, 49 multiferroics, [50][51][52][53] topological insulators, [54][55][56] and many others. In addition, a number o...…”