Charge-carrier density and interplane coupling in Y2Ba4Cu7O15: A Cu NMR-NQR study

Lack of evidence for orbital-current effects in the high-temperature Y2Ba4Cu7O15-delta superconductor using 89Y nuclear magnetic resonance

We have performed NMR measurements at the Y site on a c-axis-oriented powder sample of the cuprate superconductor Y2Ba4Cu7O15-delta to search for the possible orbital-current phase. The temperature dependence of the Y linewidth and relaxation behavior in the normal-conducting phase were studied down to 100 K. These measurements give upper limits for a static magnetic field and the amplitude of a fluctuating magnetic field at the Y site of < or approximately 0.15 and < or approximately 0.7 mT, respectively. These values provide significant constraints on possible static or quasistatic orbital currents.

Direct observation of the oxygen isotope effect on the in-plane magnetic field penetration depth in optimally doped YBa2Cu3O7-delta

We report the first direct observation of the oxygen-isotope ((16)O/(18)O) effect on the in-plane penetration depth lambda(ab) in a nearly optimally doped YBa(2)Cu(3)O(7-delta) film using the novel low-energy muon-spin rotation technique. Spin-polarized low-energy muons are implanted in the film at a known depth z beneath the surface and process in the local magnetic field B(z). This feature allows us to measure directly the profile B(z) of the magnetic field inside the superconducting film in the Meissner state and to make a straightforward determination of lambda(ab). A substantial isotope shift Delta lambda(ab)/lambda(ab)=2.8(1.0)% at 4 K is observed, implying that the in-plane effective supercarrier mass m*(ab) is oxygen-isotope dependent with Delta m*(ab)/m*(ab)=5.5(2.0)%. These results are in good agreement with magnetization measurements on powder samples.