How to reduce the cultural gap between the generations Y and Millenials? What is the best intangible motivation for Millenials?

The gap can't be removed, but actually HR services should take into account this difference in terms of motivation. Also I think that collaboration in teams could suffer in case this difference between generations is not respected.

Strange question actually, but simply because what you are describing is not a cultural gap more than an interval between each Era in a civilization.it is very natural and sorry to say that "it can't be removed or mirged"