Experiments on electron- and hole-doped high Tc copper oxide superconductors

In this paper experiments on hole-doped Y1-xPrxBa2Cu3O7-δ and electron-doped Ln2-xMxCuO4-y (Ln-Pr, Nd, Sm, Eu, Cd; M = Ce, Th; y = 0.02) compounds are briefly reviewed. The hole-doped Y1-xPrxBa2Cu3O7-δ system exhibits a rich variety of phenomena including a metal-insulator transition at x ∼ 0.6 high Tc superconductivity, anomalous behavior of the pressure dependence of Tc and the temperature dependence of the upper critical field, antiferromagnetic (AFM) ordering of Cy2+ and Pr ions, Kondo-like specific heat anomalies, and enormous electronic specific heat coefficients. The underlying cause of many of these phenomena appears to be associated with strong hybridization between the localized 4f states of Pr and the CuO2 valence band states. Investigations on the electron-doped Ln2-xMxCuO4-y compounds suggest the existence of an electron-hole symmetry in the occurrence of the metal-insulator transition, Cu2+ AFM ordering, and superconductivity as a function of electron or hole donor concentration. Recent experiments on the electron-doped Ln23-xMxCuO4-y compounds reveals an electron-hole antisymmetry in the pressure dependence of Tc and the first example of the effect of AFM ordering on superconductivity in high Tc cuprates