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The narrow band gap semiconductors Bi2Te3 and Sb2Te3 are well known for their room temperature thermoelectric performance. Recently, they were shown to serve as model systems of three‐dimensional topological insulators with a bulk band gap and very robust, spin‐resolved surface states due to a special band inversion in their periodic bulk. Evidently, it is of interest to investigate the special surface states with a local probe like nuclear magnetic resonance (NMR). However, especially the bulk NMR of these materials shows peculiar and rather unexpected phenomena, e. g., a magnetic field induced deformation of the local charge symmetry and excessive line broadening due to a special internuclear coupling. Here we report a comprehensive account of the room temperature NMR properties of the spin‐1/2 nucleus 125Te of single crystalline Bi2Te3 and Sb2Te3. This includes a very unusual spin‐lattice relaxation that seems not to be reflected in the NMR shift, as well as an exchange enhanced NMR line broadening. [ABSTRACT FROM AUTHOR]

The local distribution of electrons and holes in the CuO2 plane of the high-temperature superconducting cuprates is determined with nuclear magnetic resonance through the quadrupole splittings of 17O and 63Cu. Based on new data for single crystals of electron-doped Pr2-xCexCuO4 (x = 0, 0.05, 0.10, 0.15) as well as Nd2-xCexCuO4 (x = 0, 0.13) the changes in hole contents nd of Cu 3dx2-y2 and np of O 2pσ orbitals are determined and these account for the stoichiometrically doped charges, similar to hole-doped La2-xSrxCuO4. It emerges that while nd + 2np = 1 in all parent materials as expected, nd and np vary substantially between different groups of materials. Doping holes increases predominantly np, but also nd. To the contrary, doping electrons predominantly decreases nd and only slightly np. However, np for the electron-doped systems is higher than that in hole-doped La1.85Sr0.15CuO4. Cuprates with the highest maximum Tc's appear to have a comparatively low nd and high np. The rather high oxygen hole content of the Pr2CuO4 and Nd2CuO4 with the low nd seems to make them ideal candidates for hole doping to obtain a potentially high Tc. [ABSTRACT FROM AUTHOR]

A NMR anvil cell design is used for measuring the influence of high pressure on the electronic properties of the high-temperature superconductor YBa2Cu4O8 above the superconducting transition temperature Tc. It is found that pressure increases the spin shift at all temperatures in such a way that the pseudogap feature has almost disappeared at 63 kbar. This change of the temperature-dependent spin susceptibility can be explained by a pressure-induced proportional decrease (factor of 2) of a temperature-dependent component, and an increase (factor of 9) of a temperature-independent component, contrary to the effects of increasing doping. The results demonstrate that one can use anvil cell NMR to investigate the tuning of the electronic properties of correlated electronic materials with pressure. [ABSTRACT FROM AUTHOR]

Topological insulators constitute a new class of materials with an energy gap in the bulk and peculiar metallic states on the surface. We report on new features resulting from the bulk electronic structure, based on a comprehensive nuclear magnetic resonance (NMR) study of 77Se on Bi2Se3 and Cu0.15Bi2Se3 single crystals. First, we find two resonance lines and show that they originate from the two inequivalent Se lattice sites. Second, we observe unusual field-independent linewidths and attribute them to an unexpectedly strong internuclear coupling mediated by bulk electrons. In order to support this interpretation, we present a model calculation of the indirect internuclear coupling and show that the Bloembergen-Rowland coupling is much stronger than the Ruderman-Kittel-Kasuya-Yosida coupling. Our results call for a revision of earlier NMR studies and add information concerning the bulk electronic properties. [ABSTRACT FROM AUTHOR]