Knight Shift in Metals

(10)
1
measured –relaxation rate on Cu and O site
T
1
The relaxation rates at all four oxygen sites and
both Cu sites in a 7.0T ( 17 O) or 7.4T ( 63 Cu) field
applied along the c-axis of the oriented powder,
versus temperature, plotted on a log-log scale.
The solid lines indicate a linear relationship
between relaxation rate and temperature. The
inset emphasizes the linear temperature
dependence of oxygen relaxation above T C .
P.C. Hammel et al., Phys. Rev. Lett. 63 (1989),
1992.
Cu
O
Cu
YBa 2
Cu 3
O 6
AF correlated Cu-spins
2
2
9
Cu 3d shell, 1 electron missing S
O
full p-shell
S
O
0
Cu
1
2
Korringa relation is fulfilled for O NMR signal, but violated for Cu NMR signal.
Short range AF magnetic correlations of Cu moments persist in the
superconducting state!
Many open questions
Once more it is very important to distinguish intrinsic signal from extrinsic (i.e.
from impurity phases).