Pressure-induced oxygen ordering phenomena in high-Tc superconductors

Abstract

High-pressure experiments on polycrystalline and single-crystalline Tl2Ba2CuO6+δ with varying oxygen content reveal the existence of distinct low (70–100 K) and high (180–270 K) temperature oxygen-defect ordering processes corresponding to activation energies EA ≈ 0.25 eV and 0.7 eV, respectively. Hall effect studies show that for both processes the effect of oxygen ordering on the superconducting transition temperature Tc is the result of a transfer of hole carriers to or from the CuO2 plane. We also report the first observation of oxygen-ordering effects in TlSr2CaCu2O7−δ. Evidence is discussed for the existence of oxygen-ordering processes in YBa2Cu3O7−y at both low and high temperatures which may be responsible for the phenomena of transient and persistent photo-induced superconductivity.