Magnetic Properties Near the Surface of Cuprate Superconductors Studied Using Beta-Detected NMR

Beta-detected Nuclear Magnetic Resonance (β-NMR) uses highly spin polarized β-emitting nuclei as a probe. Besides its use in nuclear physics, it has also become a powerful and sensitive tool in condensed matter physics and materials science. At TRIUMF, β-NMR of 8Li+ has been developed to study materials in a depth-resolved manner, where the implantation depth of 8Li+ is controlled via electrostatic deceleration. In this thesis, β-NMR of 8Li+ has been used to study high-Tc cuprate superconductors (HTSC). The objective of this work is to search for spontaneous magnetic fields generated by a possible time-reversal symmetry breaking (TRSB) superconducting state near the surface of hole-doped YBa2Cu3O7−δ (YBCO), and study the nature of the vortex lattice (VL) in YBCO and electron-doped Pr2−xCexCuO4−δ (PCCO). For several advantages, our measurements were carried out by implanting 8Li+ in thin silver films evaporated on the superconductors. In our TRSB studies, the magnetic field distribution p(B) is measured 8 nm away from the Ag/YBCO interface in magnetic fields B0 = 5 to 100 G, applied parallel to the interface. p(B) showed significant broadening below the Tc of aband c-axis oriented YBCO films. The broadening signals the existence of weak disordered magnetic fields near the surface of YBCO. From the broadening’s temperature and field dependence we draw an upper limit of 0.2 G on the magnitude of spontaneous magnetic fields associated with TRSB. To study the VL, p(B) is measured at average implantation depths ranging from 20 to 90 nm away from the Ag/YBCO or Ag/PCCO interface in B0 = 0.1 to 33 kG, applied perpendicular to the surface. p(B) showed a dramatic broadening below Tc as expected from the emerging field lines of the VL in the superconductor. In YBCO, p(B) is symmetric and the de-