Measuring the Electron Spectral Function by Angle-Resolved Photoemission

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9974401CampuzanoThe goal of this project is to determine the nature of the charge carriers in the high temperature superconductors using the technique of angle-resolved photoemission (ARPES). This spectral function represents the probability of adding or removing an electron from a many-body system. In these materials, the electrons strongly interact with one another and with other collective excitations such as spin waves. The spectral function provides very useful information about these interactions. Under suitable conditions, the spectral function can be manipulated to yield the self energy of the electrons, which is the quantity directly calculable by modern theories of strongly interacting many-body systems. This work aims to study the self-energy in the different states of high temperature superconductors. This project also seeks to understand how the Fermi surface changes shape when the material undergoes the superconducting transition. Recent work by this group has found the remarkable effect that electronic states at different momenta become gapped at different temperatures, leading to a break up of the Fermi surface into disconnected Fermi arcs which shrink with decreasing T, eventually collapsing to points in the superconducting ground state below Tc. This novel behavior, where the Fermi surface does not form a continuous contour in momentum space as in conventional metals, is unprecedented in that it occurs in the absence of long range order.%%%The high temperature superconductors are materials that carry current without any resistance when cooled to the temperature of liquid air. This research using the technique of angle-resolved photoemission (ARPES) is designed help reach an understanding of how electrons move in the high temperature superconductors to carry electrical current. These new materials are unlike all previously known materials in the way they conduct electricity. Now, 10 years after their discovery, the mechanisms are still not fully understood. This work aims to connect the physical quantities measured by ARPES to quantities measured using other techniques. As aconsequence, this project provides excellent research opportunities for graduate students who wish to work at the frontier of our understanding of new materials.***