Rainer: I think the 3D Xpoint storage works with some phase change material (PCM) to store information. In PCM the crystalline structure can be changed by a current and then remains in that state without any voltage applied.

Oh, I should answer to my own post and amend that Intel and Micron did not say which kind of physical property they are using/changing to store information. So, yes, this could be a phase change, but it does not need to be PCM. It could well be something else.