  The neutron-neutron and proton-proton pairing correlations have long been
recognised to be the dominant many-body correlation beyond the nuclear mean
field since the introduction of pairing mechanism by Bohr, Mottelson and Pines
nearly 60 year ago. Nevertheless, few conclusion has been reached concerning
the existence of analogous neutron-proton (np) pair correlated state. One can
see a renaissance in np correlation studies in relation to the significant
progress in radioactive ion beam facilities and detection techniques. The np
pairs can couple isospin T = 1 (isovector) or 0 (isoscalar). In the isovector
channel, the angular momentum zero component is expected to be the most
importance one. On the other hand, as one may infer from the general properties
of the np two-body interaction, in the isoscalar channel, both the np pairs
with minimum (J=1) and maximum (J=2j) spin values can be important. In this
contribution, we will discuss the possible evidence for np pair coupling from
different perspective and analyze its influence on interesting phenomena
including the Wigner effect and mass correlations in odd-odd nuclei. In
particular, we will explain the spin-aligned pair coupling scheme and quartet
coupling involving pairs with maximum (J=2j) spin values.
