NMR study of magnetism and superconductivity in high-Tc oxides

The results of
¹³⁹
La and
⁶³
Cu nuclear quadrupole resonance (NQR) on La-Ba,Sr-Cu-O, Y-Ba-Cu-O, and Bi-Pb-Sr-Ca-Cu-O compounds and of
¹⁷
O nuclear magnetic resonance (NMR) on Y-Ba-Cu-O are extensively reviewed. As for the magnetism, the phase diagram for the La system studied by a
¹³⁹
La NQR experiment is presented, with evidence of the disordered magnetic state between the 3D-antiferromagnetic (AF) ordered state and the superconducting state. With respect to its superconducting nature, the nuclear spin-lattice relaxation behavior (T
1
) of Cu in the CuO
2
plane has been found to be unconventional above and below T
c
for all compounds, with no signatures expected for a nonmagnetic metal and a BCS superconductor, respectively. The behavior of T
1
of Cu above T
c
is shown to be dominated by AF fluctuation of Cu d spins. In contrast, an enhancement of 1/T
1
of
¹⁷
O has been observed just below T
c
, which is similar to a BCS case.