Laser based angle-resolved photoemission spectroscopy and high-temperature superconductivity

A laser based system for performing high resolution angle-resolved photoemission spectroscopy (ARPES) is presented. This system uses 6 eV photons from the fourth harmonic of a Ti:Sapphire oscillator, which increases the bulk-sensitivity of ARPES by about an order of magnitude compared to higher energy synchrotron based sources. The laser system also offers an order of magnitude improvement in both photon flux and momentum resolution. The greatly reduced operating costs of the laser ARPES system should make the ARPES technique available to researches without access to synchrotron light sources. The details of the design, construction, and calibration of all aspects of the laser ARPES system are all discussed in this thesis.;Laser ARPES is used to study the high Tc superconductor Bi2Sr2CaCu2O8+delta (Bi2212), which is perhaps the material most heavily studied with ARPES. These low energy ARPES experiments are found to be in the sudden limit for states near the Fermi surface, accurately reproducing the qualitative features seen in previous studies of this material. The improvements in resolution have facilitated the first observation of spectral peaks which are sharp on the scale of their energy---the clearest evidence yet for quasiparticles in the normal state of a high Tc superconductor. This brings ARPES measurements of the quasiparticle scattering rate into agreement with optical transport measurements for the first time. The width of these peaks in momentum space corresponds to a nodal mean free path far greater than the length scale of the gap inhomogeneity seen in scanning tunneling microscopy (STM) measurements.;The peak-dip-hump lineshape is introduced to fit the emergence of a high energy spectral hump in underdoped Bi2212. A very high resolution study of the superconducting gap symmetry is presented, revealing significant contributions to the gap from higher order d-wave harmonics in agreement with previous studies. This feature of the gap symmetry is found to likely be intrinsic to the pairing interaction, indicating an interaction range beyond nearest-neighbor lattice sites.;A linear temperature dependence to the nodal Fermi velocity is observed at all doping levels, possibly indicating a new many-body effect. Simulations of the coupling of electrons to various collective excitations indicate the qualitative requirements of the bosonic spectrum: it must contain a sharp spike in order to produce the dispersion kink, but must also possess a component which extends over a broad energy range in order to produce the linear temperature dependence of the Fermi velocity.;Above all else, the work presented here paves the way for the use of lasers as an ARPES light source. The improvements offered by this new technique, as well as the possibility to do time-resolved pump-probe ARPES, indicate a promising future for lasers in the direct study of electronic interactions in solids.