Phase Diagrams of Cuprate Superconductors – an Investigation of Competing Orders and Quantum Criticality

We present scanning tunneling spectroscopic and high-field thermodynamic studies of holeand electron-doped (pand n-type) cuprate superconductors. Our experimental results are consistent with the notion that the ground state of cuprates is in proximity to a quantum critical point (QCP) that separates a pure superconducting (SC) phase from a phase comprised of coexisting SC and a competing order, and the competing order is likely a spin-density wave (SDW). The effect of applied magnetic field, tunneling current, and disorder on the revelation of competing orders and on the low-energy excitations of the cuprates is discussed.