Splitting of the absorption edge in the topological insulator Bi1.1Sb0.9Te2S: mid-infrared magneto-optical study

M V Yakushev; T V Kuznetsova; D V Belyaev; V I Grebennikov; M Orlita; G Martinez; K A Kokh; R W Martin; O E Tereshchenko

doi:10.1088/1361-6463/adb317

Splitting of the absorption edge in the topological insulator Bi1.1Sb0.9Te2S: mid-infrared magneto-optical study

M V Yakushev, T V Kuznetsova, D V Belyaev, V I Grebennikov, M Orlita, G Martinez, K A Kokh, R W Martin, O E Tereshchenko

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Abstract

External magnetic fields can be used to control the spin properties of charge carriers in topological insulators (TIs). Thin p-type layers of the TI Bi1.1Sb0.9Te2S were studied using mid-infrared Fourier transform magneto-transmission spectroscopy in magnetic fields up to 11 T. Zero field spectra, measured at 4.2 K and 300 K, demonstrated a sharp absorption edge, used to determine an optical bandgap Egopt of 0.31 and 0.22 eV, respectively, as well as to establish the direct character of the bandgap. Fabry–Perot oscillations were used to estimate a refractive index of 6.4. A difference of Egopt from the bandgap, determined earlier by angular resolved photoelectron spectroscopy, was attributed to the formation of band tails generated by high concentrations of randomly distributed charged defects. Equal electron me and hole mh effective masses of 0.152m0 were determined using a theoretical model employing simplified Dirac-type Hamiltonian. Magnetic fields split the absorption edge and the non-linear character of this splitting energy resulted in a strong decrease of the g-factor with increasing field.

Original language	English
Article number	145101
Number of pages	7
Journal	Journal of Physics D: Applied Physics
Volume	58
Issue number	14
Early online date	18 Feb 2025
DOIs	https://doi.org/10.1088/1361-6463/adb317
Publication status	Published - 7 Apr 2025

Funding

The research was carried out within the state assignment of the Ministry of Science and Higher Education of the Russian Federation (‘Spin’ No 122021000036-3). Crystal growth was performed under the state assignment IGM SB RAS 122041400031-2. The authors acknowledge the support of the LNCMI-CNRS in Grenoble as a member of the European Magnetic Field Laboratory (EMFL). The UK authors are grateful for the travel expenses reimbursement: projects EP/X020304/1 and NS/A000060/1.

Keywords

topological insulators
Bi1.1Sb0.9Te2S
magneto-transmission
Zeeman effect
g-factor

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Yakushev, M. V., Kuznetsova, T. V., Belyaev, D. V., Grebennikov, V. I., Orlita, M., Martinez, G., Kokh, K. A., Martin, R. W., & Tereshchenko, O. E. (2025). Splitting of the absorption edge in the topological insulator Bi1.1Sb0.9Te2S: mid-infrared magneto-optical study. Journal of Physics D: Applied Physics, 58(14), Article 145101. https://doi.org/10.1088/1361-6463/adb317

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title = "Splitting of the absorption edge in the topological insulator Bi1.1Sb0.9Te2S: mid-infrared magneto-optical study",

abstract = "External magnetic fields can be used to control the spin properties of charge carriers in topological insulators (TIs). Thin p-type layers of the TI Bi1.1Sb0.9Te2S were studied using mid-infrared Fourier transform magneto-transmission spectroscopy in magnetic fields up to 11 T. Zero field spectra, measured at 4.2 K and 300 K, demonstrated a sharp absorption edge, used to determine an optical bandgap Egopt of 0.31 and 0.22 eV, respectively, as well as to establish the direct character of the bandgap. Fabry–Perot oscillations were used to estimate a refractive index of 6.4. A difference of Egopt from the bandgap, determined earlier by angular resolved photoelectron spectroscopy, was attributed to the formation of band tails generated by high concentrations of randomly distributed charged defects. Equal electron me and hole mh effective masses of 0.152m0 were determined using a theoretical model employing simplified Dirac-type Hamiltonian. Magnetic fields split the absorption edge and the non-linear character of this splitting energy resulted in a strong decrease of the g-factor with increasing field.",

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T2 - mid-infrared magneto-optical study

AU - Yakushev, M V

AU - Kuznetsova, T V

AU - Belyaev, D V

AU - Grebennikov, V I

AU - Orlita, M

AU - Martinez, G

AU - Kokh, K A

AU - Martin, R W

AU - Tereshchenko, O E

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N2 - External magnetic fields can be used to control the spin properties of charge carriers in topological insulators (TIs). Thin p-type layers of the TI Bi1.1Sb0.9Te2S were studied using mid-infrared Fourier transform magneto-transmission spectroscopy in magnetic fields up to 11 T. Zero field spectra, measured at 4.2 K and 300 K, demonstrated a sharp absorption edge, used to determine an optical bandgap Egopt of 0.31 and 0.22 eV, respectively, as well as to establish the direct character of the bandgap. Fabry–Perot oscillations were used to estimate a refractive index of 6.4. A difference of Egopt from the bandgap, determined earlier by angular resolved photoelectron spectroscopy, was attributed to the formation of band tails generated by high concentrations of randomly distributed charged defects. Equal electron me and hole mh effective masses of 0.152m0 were determined using a theoretical model employing simplified Dirac-type Hamiltonian. Magnetic fields split the absorption edge and the non-linear character of this splitting energy resulted in a strong decrease of the g-factor with increasing field.

AB - External magnetic fields can be used to control the spin properties of charge carriers in topological insulators (TIs). Thin p-type layers of the TI Bi1.1Sb0.9Te2S were studied using mid-infrared Fourier transform magneto-transmission spectroscopy in magnetic fields up to 11 T. Zero field spectra, measured at 4.2 K and 300 K, demonstrated a sharp absorption edge, used to determine an optical bandgap Egopt of 0.31 and 0.22 eV, respectively, as well as to establish the direct character of the bandgap. Fabry–Perot oscillations were used to estimate a refractive index of 6.4. A difference of Egopt from the bandgap, determined earlier by angular resolved photoelectron spectroscopy, was attributed to the formation of band tails generated by high concentrations of randomly distributed charged defects. Equal electron me and hole mh effective masses of 0.152m0 were determined using a theoretical model employing simplified Dirac-type Hamiltonian. Magnetic fields split the absorption edge and the non-linear character of this splitting energy resulted in a strong decrease of the g-factor with increasing field.

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Splitting of the absorption edge in the topological insulator Bi1.1Sb0.9Te2S: mid-infrared magneto-optical study

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