Microscopic Theory of High Temperature Superconductivity Induced by Electronic Fluctuations

University Of California-Riverside, Riverside CA

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical research on a consistent microscopic theory of the extraordinary phenomena discovered in high temperature cuprate superconductors. Work done by the PI in the past two years suggests that d-wave superconductivity in cuprates comes from the quantum-critical fluctuations of the time-reversal order parameter discovered in the pseudogap region of the phase diagram and their derived coupling to fermions. In this project, the PI will work on providing definitive evidence for this suggestion by analyzing high resolution laser-angle-resolved-photoemission-spectroscopy to determine (i) the absolute magnitudes and the momentum and frequency dependence of the spectrum of fluctuations, and (ii) their coupling to fermions and variation for a range of dopings and critical temperatures. The expected outcome is the formulation of a fundamental and testable theory of the pseudo gap. In addition to this main theme, the PI and his group will undertake two new investigations on related problems: (1) Solution of Eliashberg equations for superconductivity induced by gaussian quantum-critical fluctuations, which are expected to yield results in variance with the Bardeen-Cooper-Schieffer type formulas for the energy gap, critical temperature, and thermodynamic quantities, and (2) Derivation of the multiple Higgs or amplitude modes expected in d-wave superconductors. This award also supports the education and training of a postdoctoral research associate and a graduate student in condensed matter theory. The PI will continue his active participation and mentoring activities under the University of California Leadership Excellence in Advanced Degrees and Mentoring Summer Research Internship programs. He will also participate in the Early Academic Outreach Program at this institution targeting high school students by providing various lectures and demonstrations. NON-TECHNICAL SUMMARY This award supports theoretical research on a consistent microscopic theory of the extraordinary phenomena discovered in high temperature cuprate superconductors. These are materials discovered in the late 1980s that conduct electricity without any dissipation (no resistance, no energy loss) when they are cooled below certain critical temperatures. Even though the critical temperatures necessary for these materials to superconduct are significantly below the room temperature, they are still much higher compared to the critical temperatures of ordinary superconductors (which are close to absolute zero). Furthermore, a theory formulated in the late 1950s that explains the microscopic mechanism of superconductivity in ordinary superconductors is not adequate to explain the mechanism and physical properties of high temperature cuprate superconductors. Even though it has been 25 years since the discovery of high temperature superconductivity and many theories have been proposed, a consistent microscopic theory that explains all properties of cuprate superconductors is still missing. For the last several years, the PI and his group have been working on a theory that is consistent with most of the experimental findings. In this project, the PI will work on providing definitive evidence for his theory by analyzing the latest high resolution spectroscopy experiments. The expected outcome is the formulation of a fundamental and testable theory of an important part of the phase diagram of the cuprate superconductors. This award also supports the education and training of a postdoctoral research associate and a graduate student in condensed matter theory. The PI will continue his active participation and mentoring activities under the University of California Leadership Excellence in Advanced Degrees and Mentoring Summer Research Internship programs. He will also participate in the Early Academic Outreach Program at this institution targeting high school students by providing various lectures and demonstrations.