Spectroscopic studies of unconventional superconductivity in iron pnictides and doped topological insulators

Topological insulators and correlated electron materials such as the iron pnictides are material classes at the forefront of current experimental and theoretical endeavors in condensed matter physics. Topological insulators embody a new state of matter that was first observed experimentally through spin- and angle-resolved photoemission measurements performed over the last two years, which differs from normal matter by invariants in band structure topology rather than broken symmetry. Layered iron pnictide compounds have been discovered over the last two years to host many of the most exciting states realized by strongly correlated electron systems, including high critical temperature ("high-TC") superconductivity, orbital order and quasi-one dimensional stripe ordering. However, pnictide electronic interactions are only "moderately correlated" and therefore much more theoretically tractable than the commonly studied cuprate and manganite systems.;In this thesis, we use angle resolved photoemission spectroscopy (ARPES) to map the electronic band structure underlying unconventional superconducting states in pnictide Ba1-xK xFe2As2 and the doped topological insulator CuxBi2Se3. Both materials have multi-orbital ("orbital-textured") Fermi surfaces that add complexity to the Cooper pairing interaction, and both feature the superconducting state in a quasi-two dimensional setting. We present detailed ARPES measurements on each compound at optimal superconducting doping, focusing on characteristics of the electron kinetics that provide the setting for a superconducting ground state, such as the detailed Fermi surface, Fermi velocities, and the presence of dispersion "kinks". These properties allow immediate insight into important parameters such as the coherence length of the superconducting wavefunction, which is unusually short for the iron pnictides, and the strength of low energy interactions that may lead to Cooper pairing. Observation of the momentum space distribution of the superconducting gap in Ba1- xKxFe2As2 also allows detailed analysis of potential interactions between specific Fermi surface regions, and can be qualitatively understood through a s+/- order parameter picture.;The measurements presented in this thesis constitute the first photoemission-based experimental exploration of properties related to superconducting and magnetic symmetry breaking in doped topological insulators. Careful observation of the surface and bulk band structure in CuxBi 2Se3 shows that the topologically insulator surface state is fully preserved at the Fermi surface under superconducting doping, establishing the first known realization of a form of superconductivity with distinctive properties derived from strong Z2 topological order.