Electron Dynamics in High Temperature Superconductors Studied Using Angle and Time-Resolved Photoemission Spectroscopy

High-Temperature Superconductivity (HTSC) has inspired decades of research since its discovery in 1986 but remains an enigmatic subject to this day. At the heart of this difficulty is the highly correlated electronic behavior that limits the usefulness of modern theoretical calculations. Angle-Resolved Photoemission Spectroscopy (ARPES) has proved an invaluable tool in the study of HTSC because it can directly measure this correlated behavior through its effects on the electronic scattering rate. However, the electronic scattering rates extracted by conventional ARPES analysis techniques can be up to an order of magnitude larger than those measured by other techniques (such as optical spectroscopy). In this work we show how this discrepancy can be explained by a combination of nanoscale electronic disorder and photoelectron surface scattering. Further, with the help of numerical modeling, we can remove these extraneous scattering events and reveal the true many-body interactions in these materials. We confirm these results by performing a systematic study of the effects of magnetic Fe impurities on the electronic structure of the HTSC Bi2Sr2CaCu2O8+δ. The second half of this thesis is devoted to the development and use of a time-resolved ARPES (trARPES) system to study these electron dynamics directly in the time domain. This allows us to measure the nonequilibrium electron dynamics, providing complementary information to normal ARPES measurements. We find that the electron dynamics are drastically slowed by the presence of the superconducting condensate and have a complex energy and momentum structure. By modeling the electrons' behavior as following an ultrafast ''pseudo-temperature'' we can explain the dynamics observed with trARPES and gain new insight into the complicated electronic behavior present in these novel materials