  One of the great achievements performed by Jacques Friedel in France has been
to promote experimental activities on the electronic properties in condensed
matter physics, which has led him, among others, to be an active promoter of
the up-rise of the "Laboratoire de Physique des Solides" (LPS). A selective
presentation of some of the work achieved in my Nuclear Magnetic Resonance
(NMR) group allows me to underline the importance of the initial choices done
by J. Friedel for the LPS. I give here an updated review of the work done on
Kondo effect in the 1970's which has allowed me to enlighten the real interest
of the NMR probe as a local experimental technique to visualize the
perturbation brought by impurities in normal metals. In a second part I
summarize the early NMR experiments done in the high Tc cuprates which have
given evidence for the existence of strong electronic correlations and
established the occurrence of the "pseudogap", on which I have initially had
some exchanges with J. Friedel. The pseudogap, occurring below a temperature
T*, has during the last twenty years raised endless discussions about the
incidence of correlations on superconductivity. Many researchers are still
advocating today that the pseudogap is due to the existence of preformed pairs
above Tc. Its robustness to impurities and disorder that we evidenced from the
early days rather suggested that it results from a competing order of the
correlated state. This is apparently better accepted nowadays, although various
distinct ordered states detected below T* are not yet understood. I also
underline the large contrast between the scientific behaviours which prevailed
between these two periods of scientific activity. I suggest that these changes
might have a negative incidence, in my opinion, on the research and education
system, at least in our field of science.
