UC Berkeley

With more than a quarter century of study, the high temperature superconducting cuprates still represent one of the most active areas of research in condensed matter physics. Its complex phase diagram continues to present challenges to our understanding, stemming from its correlated electronic nature. Being able to tease out the effect of different lattice orderings and their effects on electronic states may be crucial to understanding the physics of the cuprates where such orderings may be crucial to the phase diagram. Thus, because of its ability to directly probe electronic band structure, Angle Resolved Photoemission Spectroscopy (ARPES) is an ideal probe to study the effects of competing orders on electronicstates near EF.

This thesis will be organized in the following way. Chapter 1 provides a broad introduction to the physics central to our work including concepts of band structure and Fermi liquid theory, as well as more exotic phenomena explored throughout the thesis. Chapter 2 introduces the ARPES technique, how it is physically understood via concepts like Green's functions, and traditional methods of data analysis. Chapter 3 explores magnetic ordering and its effect on both core level and valance band states in the iron oxypnictides. From the near-EF electronic states, we find that the magnetic physics of the parent compound may still be present even at superconducting dopings. Chapter 4 explores charge density wave (CDW) ordering by looking at the rare earth ditellurides. This ARPES work establishes LaTe2 as the first quasi-2D CDW system to behave like a true Peierls transition, with both Fermi surface nesting tied to a metal - to - insulating transition. Chapter 5 explores the effect

of lattice strain on electronic states by studying the single layered Bi2201 cuprates with lanthanide substitution. The effect of this substitution competes with superconductivity and appears to enhance bosonic modes acting on the nodal point states which are otherwise unaffected. Chapter 6 takes the specific case of Nd-Bi2201 and finds evidence of a distinct crossover point in the electronic states near EF segregating the nodal point states. Finally, Chapter 7 provides a summary of our work and its conclusions.