Abstract The indirect spin-spin coupling is a molecular internuclear interaction, which is observable by utilizing NMR spectroscopy. This coupling, denoted J, is a second-order tensorial property that consists of rank-0, 1, and 2 components. The present thesis deals with the experimental determination of the rank-0 and rank-2 components of J tensors for different pairs of interacting nuclei by utilizing liquid crystal NMR (LC NMR) method. The experimental information of the rank-2 component of the J tensor appears as Janiso, a combination of tensor elements. In LC NMR, Janiso is manifested as a contribution to the experimental anisotropic coupling (Dexp ) that contains also the corresponding internuclear dipolar coupling, D. The dipolar coupling is defined by the molecular geometry and average orientation, and affected by the molecular motions. Therefore, the molecular geometry and orientation have to be determined together with the studied Janiso couplings. The contributions to D couplings arising from the molecular vibrations and solvent-induced deformation of the molecular geometry are taken into account in the analysis of the experimental data; the contributions are presented briefly in this thesis. The LC NMR experiments are performed for C6H6, HCONH2, C2H2, C2H4, C2H6, 1,4-C6H4F2, CH3F, CH2F2, CHF3, and CSiH6 molecules, and some important aspects of the liquid crystal NMR method are discussed. The obtained information of J tensors is compared with the theoretical ab initio MCSCF results. Finally, the systematics of the J tensors in different structural surroundings is found and the significance of the indirect contribution to the corresponding Dexp coupling is discussed.

Die drei-dimensionalen Topologische Isolatoren Bi2Se3 and Bi2Te3 sind Modell-Systeme einer neuen Klasse von Isolatoren mit metallischen Oberflächenzuständen. Ihre kleinen Bandlücken und die schweren Elemente sind essentiell für die topologisch nicht-triviale Bandstruktur, sind aber ebenso verantwortlich für andere bemerkenswerte Eigenschaften, wie etwa für ihre Leistungsfähigkeit als Thermoelektrika. Diese Arbeit untersucht die elektronischen Eigenschaften der Topologischen Isolatoren Bi2Se3 und Bi2Te3 mittels zahlreicher experimenteller Methoden. Es wird gezeigt, dass Ferromagnetismus in Mn gedoptem Bi2Te3 durch sintern unterdrückt werden kann. Zudem werden ein überraschend großer Magnetoresistiver Effekt und ein ladungsträgerunabhängiger Vorzeichenwechsel des Seebeck-Koeffizienten mit zunehmenden Mn Gehalt diskutiert. Kernmagnetische Resonanz (NMR) von 125Te Kernen in Bi2Te3 Einkristallen lässt auf eine ungewöhnliche elektronische SpinSuszeptibilität and komplexe NMR Verschiebungen schließen. Es wird gezeigt dass die Quadrupolwechselwirkung von 209Bi Kernen in Bi2Se3 Einkristallen eine Signatur der Bandinversion ist, in quantitativer Ubereinstimmung mit DFT Rechnungen. Weiterhin wird argumentiert dass die starke Spin-Bahn Kopplung der Leitungselektronen zu einer nicht-trivialen Orientierungsabh¨angigkeit der 209Bi Quadrupolaufspaltung führt.:Contents List of Figures List of Tables List of abbreviations Introduction 1 Topological insulators in three dimensions 2 Theoretical background 3 Methods I: structural, electronic and magnetic properties 4 Methods II: nuclear magnetic resonance 5 Sample preparation and basic characterisation6 Magnetic and electronic properties of Mn doped Bi2Te3 7 NMR of spin 1/2 nuclei: 125Te in Bi2Te3 8 NMR of quadrupole nuclei: 209Bi in Bi2Se3 Conclusions and outlook Appendix Bibliography / The three-dimensional topological insulators Bi2Se3 and Bi2Te3 are model systems of a new class of materials with an insulating bulk and gapless surface states. Their small band gaps and the heavy elements are essential for the topologically non-trivial band structure, but these features are similarly responsible for other remarkable properties, such as their high thermoelectric performance. This thesis investigates the electronic properties of the topological insulators Bi2Se3 and Bi2Te3 with a broad range of experimental methods. Ferromagnetism in Mn doped Bi2Te3 is shown to disappear under sample sintering. A surprisingly large magnetoresistance and a charge carrier independent change in the sign of the thermopower with increasing Mn content are discussed.125Te nuclear magnetic resonance (NMR) of Bi2Te3 single crystals suggest an unusual electronic spin susceptibility and complex NMR shifts. The quadrupole interaction of 209Bi nuclei in Bi2Se3 single crystals is shown to be a signature of the band inversion in quantitative agreement with first-principle calculations. Furthermore, it is proposed that the strong spin-orbit coupling of conduction electrons causes a non-trivial orientation dependent quadrupole splitting of the 209Bi resonance.:Contents List of Figures List of Tables List of abbreviations Introduction 1 Topological insulators in three dimensions 2 Theoretical background 3 Methods I: structural, electronic and magnetic properties 4 Methods II: nuclear magnetic resonance 5 Sample preparation and basic characterisation6 Magnetic and electronic properties of Mn doped Bi2Te3 7 NMR of spin 1/2 nuclei: 125Te in Bi2Te3 8 NMR of quadrupole nuclei: 209Bi in Bi2Se3 Conclusions and outlook Appendix Bibliography