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Infrared magneto-spectroscopy of Bi2Te3 topological insulator
Mohelský, Ivan ; Výborný, Karel (referee) ; Orlita, Milan (advisor)
Tato práce se zabývá charakterizací topologického izolátoru Bi2Te3, materiálu s nevodivými stavy v objemu, ale jedním vodivým pásem na povrchu. Tento materiál je zkoumán již přes 60 let, ale i přes to není jeho objemová pásová struktura úplně objasněna, obzvláště charakter zakázaného pásu je stále předmětem diskuze. V této práci jsou prezentovány výsledky infračervené spektroskopie na Landauových hladinách v magnetickém poli až do 34 T, doplněné elipsometrickým měřením mimo magnetické pole. Výsledky těchto měření by měli pomoci vyjasnit některé vlastnosti zakázaného pásu. Pozorovaná optická odezva odpovídá polovodiči s přímým zakázaným pásem, ve kterém se nosiče náboje chovají jako Diracovské hmotné fermiony. Šířka zakázaného pásu za nízkých teplot byla určena jako Eg = (175±5) meV a samotný zakázaný pás se nachází mimo trigonální osu, tím pádem se v první Brillouinově zoně vyskytuje 6 krát nebo 12 krát.
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Zeemanův jev v polovodičových kvantových strukturách
Stráský, Josef ; Grill, Roman (advisor) ; Výborný, Karel (referee)
This theoretical thesis presents detailed study of negatively charged excitons - trions - confined in single quantum well in presence of perpendicular magnetic field. Complex valence band of GaAs/GaAlAs compound is described within Luttinger Hamiltonian framework. Singlet and triplet states of negative trion are introduced. Advanced theoretical analysis of Zeeman effect for different states of trion is performed. Landau gauge of magnetic field and unusual wavefunctions basis is chosen and its accuracy is tested. Evolution of ground state energy and photoluminescence spectra with magnetic field is evaluated for different values of Landé g-factors. Probability of occurrence of electrons with respect to the hole position and their spatial correlation function are investigated.
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Optical and magneto-optical studies of ferrimagnetic garnets for photonic and spintronic applications
Beran, Lukáš ; Veis, Martin (advisor) ; Dubroka, Adam (referee) ; Výborný, Karel (referee)
Title: Optical and magneto-optical studies of ferrimagnetic garnets for photonic and spintronic applications Author: RNDr. Lukáš Beran Department: Intitute of Physics of Charles University Supervisor: RNDr. Martin Veis, PhD., Institute of Physics of Charles University Abstract: This doctoral thesis is devoted to fabrication and systematic char- acterization of physical properties of thin films of iron garnets with potential applications in photonic and spintronic devices. Investigated samples were pre- pared by metallo-organic decomposition and pulsed laser deposition. The study was focused on structural and magnetic characterizaiton along with optical and magneto-optical properties. Obtained experimental results were further con- fronted with theoretical calculations. The application potencial of garnets for photonic devices was discussed based on determined Figure of Merit (Faraday rotation to optical loss ratio). High values were achieved for single crystal thin film of Ce doped yttrium iron garnet on galium gadolinium garnet substrate as well as for pollycrystalline Bi doped yttrium iron garned on silicon substrate. Furthermore, new rare-earth garnets were prepared with attempt to achieve per- pendicular magnetic anisotropy of these film. This was achieved for three di erent materials, which were not...
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Development of extracellular-matrix scaffolds for CNS repair
Výborný, Karel ; Kubinová, Šárka (advisor) ; Hampl, Aleš (referee) ; Vandrovcová, Marta (referee)
Výborný, Karel. Vývoj materiálů na bázi extracelulární matrix pro léčbu centrálního nervového systému. [Development of extracellular-matrix scaffolds for CNS repair]. Praha, 2020. 105 stran, 3 přílohy. Dizertační práce (Ph.D.). Univerzita Karlova, 2. lékařská fakulta, Ústav experimentální medicíny, AV ČR v.v.i. Abstract Brain and spinal cord injury are a serious traumata and despite intensive research, there is still no effective treatment for patients. One of the studied approaches is to use various biomaterials to repair the damaged neural tissue. The aim of this thesis is to study the regenerative and neurotrophic effects of injectable extracellular matrix (ECM) hydrogels prepared by decellularization from porcine tissue (brain, spinal cord, bladder) and human umbilical cord (UC) in reconstruction of damaged neural tissue of the brain and spinal cord in rats. We characterized ECM hydrogels in terms of mechanical and rheological properties, structure and composition, cell adhesion, migration and proliferation. In a model of spinal cord hemisection, we compared the regenerative effect of ECM hydrogels derived from porcine spinal cord and urinary bladder. We found no benefits of tissue specific ECM prepared from the tissue of neural origin in terms of its neurotrophic properties in vitro or in vivo....
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Optical and magneto-optical studies of ferrimagnetic garnets for photonic and spintronic applications
Beran, Lukáš ; Veis, Martin (advisor) ; Dubroka, Adam (referee) ; Výborný, Karel (referee)
Title: Optical and magneto-optical studies of ferrimagnetic garnets for photonic and spintronic applications Author: RNDr. Lukáš Beran Department: Intitute of Physics of Charles University Supervisor: RNDr. Martin Veis, PhD., Institute of Physics of Charles University Abstract: This doctoral thesis is devoted to fabrication and systematic char- acterization of physical properties of thin films of iron garnets with potential applications in photonic and spintronic devices. Investigated samples were pre- pared by metallo-organic decomposition and pulsed laser deposition. The study was focused on structural and magnetic characterizaiton along with optical and magneto-optical properties. Obtained experimental results were further con- fronted with theoretical calculations. The application potencial of garnets for photonic devices was discussed based on determined Figure of Merit (Faraday rotation to optical loss ratio). High values were achieved for single crystal thin film of Ce doped yttrium iron garnet on galium gadolinium garnet substrate as well as for pollycrystalline Bi doped yttrium iron garned on silicon substrate. Furthermore, new rare-earth garnets were prepared with attempt to achieve per- pendicular magnetic anisotropy of these film. This was achieved for three di erent materials, which were not...
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Infrared magneto-spectroscopy of Bi2Te3 topological insulator
Mohelský, Ivan ; Výborný, Karel (referee) ; Orlita, Milan (advisor)
Tato práce se zabývá charakterizací topologického izolátoru Bi2Te3, materiálu s nevodivými stavy v objemu, ale jedním vodivým pásem na povrchu. Tento materiál je zkoumán již přes 60 let, ale i přes to není jeho objemová pásová struktura úplně objasněna, obzvláště charakter zakázaného pásu je stále předmětem diskuze. V této práci jsou prezentovány výsledky infračervené spektroskopie na Landauových hladinách v magnetickém poli až do 34 T, doplněné elipsometrickým měřením mimo magnetické pole. Výsledky těchto měření by měli pomoci vyjasnit některé vlastnosti zakázaného pásu. Pozorovaná optická odezva odpovídá polovodiči s přímým zakázaným pásem, ve kterém se nosiče náboje chovají jako Diracovské hmotné fermiony. Šířka zakázaného pásu za nízkých teplot byla určena jako Eg = (175±5) meV a samotný zakázaný pás se nachází mimo trigonální osu, tím pádem se v první Brillouinově zoně vyskytuje 6 krát nebo 12 krát.
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Magneto-optical study of antiferromagnetic materials for spintronics
Kubaščík, Peter ; Němec, Petr (advisor) ; Výborný, Karel (referee)
The main goal of this thesis was to develop an experimental technique for investigation of ferromagnetic and antiferromagnetic materials using magneto-optical effects that are quadratic in magnetization. Using a prototype of 2-dimensional electromagnet, which enables to rotate magnetic field of constant magnitude in the sample plane, we were able to study spectral dependences and anisotropies of corresponding magneto-optical coefficients. In ferromagnetic semiconductor GaMnAs we revealed that the anisotropy of Voigt effect magneto-optical coefficient is strongly wavelength dependent - this coefficient can be both isotropic and anisotropic. Very strong anisotropy of this coefficient was observed for metallic FeRh in a ferromagnetic state. Finally, a new method that can be used to measure Voigt effect in antiferromagnetic state of FeRh was demonstrated.
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Linear terahertz spectroscopy of semiconductor nanostructures
Kadlec, Josef ; Ostatnický, Tomáš (advisor) ; Výborný, Karel (referee)
In this thesis there is used quantum model of electron conductivity of semiconductor nanostructures introduced in [4].Conductivity is calculated in first order perturbation theory with addition of thermalization current. Main focus of this thesis is concerned on calculation of conductivity of crystal shaped full or hollow sphere with use of above mentioned model. Calculated equation is then used for numerical calculation of conductivity spectra of GaAs in terahertz region, that is then graphically visualised.
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Zeemanův jev v polovodičových kvantových strukturách
Stráský, Josef ; Grill, Roman (advisor) ; Výborný, Karel (referee)
This theoretical thesis presents detailed study of negatively charged excitons - trions - confined in single quantum well in presence of perpendicular magnetic field. Complex valence band of GaAs/GaAlAs compound is described within Luttinger Hamiltonian framework. Singlet and triplet states of negative trion are introduced. Advanced theoretical analysis of Zeeman effect for different states of trion is performed. Landau gauge of magnetic field and unusual wavefunctions basis is chosen and its accuracy is tested. Evolution of ground state energy and photoluminescence spectra with magnetic field is evaluated for different values of Landé g-factors. Probability of occurrence of electrons with respect to the hole position and their spatial correlation function are investigated.
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