Говорят, что меняют сопротивление материала между электродами. Отказываются говорить, что это за чудо-материал. http://www.wired.com/2015/07/3d-xpoint/
http://www.bbc.com/news/technology-33675734
3D XPoint works by changing the properties of the material that makes up its memory cells to either having a high resistance to electricity to represent a one or a low resistance to represent a zero.
Intel and Micron declined to describe the materials they used in creating 3D XPoint, saying that for the moment, those details are proprietary.