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Infrared magneto-spectroscopy of the Rashba-type semiconductors
Šikula, Marek ; Dubroka, Adam (oponent) ; Orlita, Milan (vedoucí práce)
Optical response of BiTeX (X = I, Cl, Br) semiconductors with a giant Rashba-type spin splitting is studied at low temperatures up to high magnetic fields applied in the Faraday configuration. Unlike the reflection configuration, the transmission configuration allows us to directly observe a set of inter-Landau level transitions in the vicinity of the crossing point of the conduction bands - Dirac point. Optical response of BiTeX compounds is compared with that expected theoretically, calculated using a simple Rashba-type Hamiltonian within Kubo-Greenwood formalism.
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Infrared magneto-spectroscopy of Bi2Te3 topological insulator
Mohelský, Ivan ; Výborný, Karel (oponent) ; Orlita, Milan (vedoucí práce)
The main goal of this thesis is to characterize the electronic band structure of Bi2Te3 topological insulator, a system that is, in an ideal case, insulating in bulk but conducting via metallic surface states. This material has been extensively studied for more than 60 years, however, its bulk band structure is not yet fully understood, especially the characteristics of the band gap are still a matter of discussion. In this thesis, results of a Landau level spectroscopy in magnetic fields up to 34 T, supplemented by ellipsometry at zero magnetic field, are presented to clarify some of the band gap properties. The observed response is consistent with the picture of a direct-gap semiconductor in which charge carriers closely resemble massive Dirac particles. The fundamental band gap reaches Eg = (175±5) meV at low temperatures, and it is not located on the trigonal axis, thus displaying either six or twelvefold valley degeneracy.
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Development of Fourier Transform InfraRed Spectroscopy in High Magnetic Fields
Dubnická Midlíková, Jana ; Marsik, Přemysl (oponent) ; Schnegg, Alexander (oponent) ; Neugebauer, Petr (vedoucí práce)
Fourier-transform infrared (FTIR) spectroscopy in high magnetic fields, concisely FTIR magneto-spectroscopy, is a powerful spectroscopic technique used to investigate many important effects in materials, e.g., electron paramagnetic resonance, cyclotron resonance, and transitions between Landau levels. Despite their enormous potential in solid-state physics, infrared magneto-spectrometers are still relatively rare and custom-made since such systems generally require complex infrastructure. This doctoral thesis describes in detail the design and implementation of a versatile FTIR magneto-spectroscopic setup operating in the range of 50 – 10 000 cm-1, high magnetic field up to 16 T and temperatures between 2 – 320 K located at the Central European Institute of Technology of Brno University of Technology. This setup allows us to perform a variety of magneto-optical measurements spanning the range from THz/far-infrared (FIR) to near-infrared (NIR). It consists of a commercial FTIR spectrometer coupled to a 16 T cryogen-free superconductive magnet by the custom-designed optical coupling and transmission probes designed for experiments with multiple detectors and samples in Faraday geometry. The novelty of the setup lies in the usage of a cryogen-free superconducting magnet. We have optimized and tested the performance of the FTIR magneto-spectroscopic setup for various configurations and determined a workable setup range. The functionality of the FTIR magneto-spectroscopic setup was demonstrated by the magneto-optical measurements of the zero-field splitting in cobalt(II)-based single ion magnet in the FIR region, indirect inter-band transitions between Landau levels (LLs) in germanium in the NIR region, and inter-band transitions between LLs in graphene in the FIR region. Moreover, we measured the I-V characteristics of graphene bolometer devices.
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Optical and magneto-optical properties of thin films of topological insulator Bi2Se3
Jambrich, Jakub ; Veis, Martin (vedoucí práce) ; Hamrle, Jaroslav (oponent)
Významným objektom výskumu v oblasti materiálov sa v posledných dvoch desaťročiach stali topologické izolátory. Ich hlavnou výhodou je, že sa na ich povrchu vytvárajú metalické vodivé stavy, v ktorých sa elektróny dokážu pohybovať, akoby ich efektívna hmotnosť bola takmer nulová. Táto vlasnosť má obrovský potenciál na využitie v novej generácii vysokorýchlostnej elektroniky. V tejto práci sa venujeme skúmaniu optických a magnetooptických vlastností topologického izolátoru Bi2Se3, ktoré sú kľúčové pre jeho ďalšie potenciálne využitie. Pomocou merania absorpcie na Landauových hladinách vo vysokom magnetickom poli určíme tvar disperzie elektrónovej štruktúry, ako aj šírku zakázaného pásu. Následne spektroskopickou elipsometriou v rozsahu viditeľného a blízkeho ultrafialového spektra odmeriame energetickú závislosť komplexnej relatívnej permitivity, ktorá je kľúčová pre popis optických vlastností.
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Infrared magneto-spectroscopy of Bi2Te3 topological insulator
Mohelský, Ivan ; Výborný, Karel (oponent) ; Orlita, Milan (vedoucí práce)
The main goal of this thesis is to characterize the electronic band structure of Bi2Te3 topological insulator, a system that is, in an ideal case, insulating in bulk but conducting via metallic surface states. This material has been extensively studied for more than 60 years, however, its bulk band structure is not yet fully understood, especially the characteristics of the band gap are still a matter of discussion. In this thesis, results of a Landau level spectroscopy in magnetic fields up to 34 T, supplemented by ellipsometry at zero magnetic field, are presented to clarify some of the band gap properties. The observed response is consistent with the picture of a direct-gap semiconductor in which charge carriers closely resemble massive Dirac particles. The fundamental band gap reaches Eg = (175±5) meV at low temperatures, and it is not located on the trigonal axis, thus displaying either six or twelvefold valley degeneracy.
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Infrared magneto-spectroscopy of the Rashba-type semiconductors
Šikula, Marek ; Dubroka, Adam (oponent) ; Orlita, Milan (vedoucí práce)
Optical response of BiTeX (X = I, Cl, Br) semiconductors with a giant Rashba-type spin splitting is studied at low temperatures up to high magnetic fields applied in the Faraday configuration. Unlike the reflection configuration, the transmission configuration allows us to directly observe a set of inter-Landau level transitions in the vicinity of the crossing point of the conduction bands - Dirac point. Optical response of BiTeX compounds is compared with that expected theoretically, calculated using a simple Rashba-type Hamiltonian within Kubo-Greenwood formalism.
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